CBDE 無料問題集「Blockchain BTA Certified Blockchain Developer - Ethereum」

（A）to sum up all ethers sent from that address.

（B）to have an additional checksum for transactions.

（C）to protect against replay attacks.

（A）to bytecode that can't be understood by humans.

（B）to bytecodes which are essentially opcodes running instruction by instruction.

（A）will return false on error while address.transfer() will cascade transactions.

（B）will cascade exceptions and address.transfer() will return a false on error.

（A）is generally possible, but currently works only in Remix, but doesn't work in Truffle.

（B）works across all compilers and platforms the same way.

（A）would be better, because it can reduce the amount of energy needed for mining.

（B）would be worse, because it would increase the amount of energy needed for mining.

（A）a function that is marked as internal cannot be called by other contracts, unless the function is used by a derived contract. Private Functions cannot be called by any other outside contract and public variables are generating automatically a getter function.

（B）a function that is marked as external can never be called internally. Private functions can also be called by derived contracts using inheritance. Private variables are accessible also in derived contracts.

（A）to use it only for things which need the benefits of the blockchain.

（B）to use it for the whole business logic. It's always best to have everything in once place.

（A）the timestamp can be influenced by a miner to a certain degree but it's always independent from the time-zone.

（B）the timestamp is based on the time zone of the miner, that is why it changes the difficulty continuously to reflect network latency.

（C）the timestamp can't be influenced by a miner and is generally considered safe to be used for randomness on the blockchain.

（A）are used primarily for debugging exceptions in solidity.

（B）are stored on chain and are a great way to get a return value when a contract calls another contract.

（C）are stored in something like a side-chain and cannot be accessed by contracts.

（A）Keccack256 while internally to hash values it's easy to use the Dagger-Hashimoto to create a meaningful hash.

（B）the Dagger-Hashimoto hashing while internally the EVM uses SHA256 which is an alias for Keccack256.

（C）the Dagger-Hashimoto hashing while internally the EVM uses Keccack256 which is almost similar to SHA256, but has a different padding so produces different hashes.