坚固测试

In the Solidity code provided, there are two contracts: MainContract and HelperContract. MainContract uses delegatecall to execute a function in HelperContract. Carefully analyze the code and determine the outcome of specific operations.

After deploying both contracts and setting the HelperContract address in MainContract, what will be the result of calling setHelperVars(100) from an EOA (Externally Owned Account)?

A: Only HelperContract's state is modified.
B: Only MainContract's state is modified.
C: States of both MainContract and HelperContract are modified.
D: Transaction fails due to the onlyOwner modifier in MainContract.
E: MainContract's sender and value are modified, but num remains unchanged.
F: HelperContract's sender and value are modified, but num remains unchanged.

Review the following Solidity code:

We want to add a fallback function to the contract. Pick the correct fallback function and correct statements:

E: Fallback function is executed if contract receives plain Ether without any data
F: Fallback function is executed if caller calls a function that is not available
G: If multiple unnamed functions are defined for a contract, the cheapest function is used as fallback function

Review the following Solidity code:

Pick the correct statements:

A: private increment function defined in contract_e is accessible in derived contract d_c but not accessible outside the derived contracts.
B: private increment function defined in contract_e is accessible only inside contract_e and not accessible to derived contracts as well.
C: internal variable str defined in contract_e is accessible in derived contract d_b but not outside the derived contracts.
D: internal variable str defined in contract_e is accessible only inside contract_e and not accessible to derived contracts as well.

You are reviewing a set of two interacting Solidity smart contracts, `ContractA` and `ContractB`. `ContractA` calls a function in `ContractB`, which in turn updates state variables in both contracts. Your task is to determine the correct behavior and gas usage implications based on the pseudo code provided:

The contracts are deployed correctly, and `ContractB` is initialized with the address of `ContractA`. Consider what happens when `incrementBoth` function of `ContractB` is called.

A: Only `ContractB`'s count is incremented; `ContractA`'s count remains unchanged.
B: Both `ContractA` and `ContractB`'s counts are incremented, with higher gas costs due to inter-contract calls.
C: Transaction fails due to lack of error handling in `ContractB`.
D: Gas optimization is achieved due to internal transaction handling.
E: `ContractA`'s count is incremented twice due to recursive call.
F: `ContractA`'s count is not incremented due to `external` keyword restriction.

A 51% attack is perhaps the most discussed threat to any public Blockchain asset. A 51% attack happens when a certain miner or mining pool, that owns more than 50% of all the network’s hashing power, acts maliciously to disturb the network’s operation.

For example: Two Bitcoin Cash mining pools, carried out a 51% attack on the Bitcoin Cash blockchain in order to stop an unknown miner from taking coins that they weren’t supposed to have access to, while the network forked.

Which of the following CAN be done by a miner employing a 51% attack?

A: Double spend their coins
B: Reverse confirmed transactions
C: Steal funds from a certain address
D: Prevent transactions from being confirmed
E: Create false transactions that never happened

Breed Chasing, solo engineer is planning to create new cryptocurrency, NEWCRAIGLIST and build a blockchain that facilitates buying and selling second-hand items with NEWCRAIGLIST from each other. Breed expects the platform to be used for international transactions and devised the following process:

- Before a transaction is considered complete, the purchaser must put the funds in an escrow service
- The sender must enter the courier tracking number into that same escrow

Palmart, toy store giant in US is asked by lawmakers to provide evidence that proves the store’s toys are not produced through child labour. Palmart’s toys are transferred between 7 parties between creation and placement at the store. Palmart is considering using blockchain to solve this problem. Discretion in the reading and writing of transactions is highly important to the store chain to protect its proprietary interests. Review the following possible solutions and pick the best approach that solves Palmart’s problem:

Option A:
Use a public blockchain that supports assets.
Then create a new toy asset for each item created. 
When the toy is transferred to the next party, mandate that the associated blockchain asset to be transferred to the next party's blockchain account with required metadata.
Lawmakers can now view transactions and transfers at any time.

Option B: 
Use a permissioned blockchain.
Require that every party involved in the process to host a node on the Palmart's network. 
Create a new toy asset for each item created. 
When the toy is transferred to the next party in the process, have the previous party use a web portal to initialize a chain code Smart Contract to transfer control of the asset. 
When the next party receives the asset have them use a web portal to initialize a chain code Smart Contracts to acknowledge receipt of the asset. 
Provide read-only permissions to the lawmakers so they can receive the evidence they are looking for.

Consider a blockchain ecosystem where a decentralized application (dApp) is designed to operate across two different blockchains: Blockchain A, which uses a unique smart contract language and execution environment, and Blockchain B, which supports Ethereum Virtual Machine (EVM) compatible smart contracts. The dApp includes a cross-chain functionality where certain actions triggered in Blockchain A's smart contract result in specific operations in a smart contract on Blockchain B. The interoperability is facilitated through a decentralized oracle that verifies and relays information between the two blockchains. Given this setup, which of the following statements most accurately reflects the challenges and considerations in implementing this dApp's cross-chain functionality?

A: Cross-chain functionality cannot be achieved due to the different smart contract languages and execution environments.
B: The decentralized oracle introduces a single point of failure, compromising the security of the dApp.
C: Synchronizing state between the two blockchains is seamless and does not introduce any additional latency.
D: The dApp can maintain consistency and atomicity in transactions across the blockchains, but it faces challenges in data validation and oracle reliability.
E: Smart contract execution on Blockchain B is entirely dependent on the state of the smart contract on Blockchain A.
F: The interoperability poses no significant challenges, as EVM compatibility ensures seamless cross-chain communication.

A new cryptocurrency, CryptoX, has a fixed total supply of 100 million tokens. Its initial release of 40 million tokens is distributed as follows: 10 million for development, 15 million for a decentralized autonomous organization (DAO) treasury, and 15 million for staking rewards. The remaining 60 million tokens are locked, with a scheduled release decreasing by 10% each year. CryptoX also has a deflationary mechanism where 0.1% of each transaction is burned.

During a market downturn, CryptoX's price drops by 30% in a month. Market analysis attributes this drop primarily to increased token selling by short-term holders, influenced by a broader market downturn in cryptocurrencies. CryptoX's community is considering responses to stabilize the price and reassure long-term investors. Two strategies are proposed:

1) Increase the transaction burn rate to 0.2%, hoping to reduce the circulating supply faster and create a deflationary pressure.
2) Maintain the current tokenomics, believing that the downturn is part of normal market fluctuations and that the existing mechanisms are robust enough for long-term stability.

Given the market analysis and the nature of the downturn, which strategy is more likely to effectively stabilize CryptoX’s price while maintaining long-term value?

A: Increase the transaction burn rate to 0.2%.
B: Maintain the current tokenomics without any changes.
C: Temporarily suspend the transaction burn mechanism.
D: Increase the release rate of the locked tokens.
E: Implement a dynamic burn rate that adjusts with market conditions.
F: Introduce a temporary buyback and burn program.