Free Blockchain CBDE Practice Exam with Questions & Answers

Name: How to Pass CBDE Exams
Brand: Examstrack
SKU: cbde
Price: 42 USD
Availability: InStock

Questions 1

If you are starting a new ERC20 token:

Options:

it would be best to start from scratch, just looking at the required interface.

it is beneficial to copy and paste the already existing code from the Ethereum wiki and modify this until you like it.

best is to start with an audited implementation, for example from OpenZeppelin, in order to reuse already existing code.

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Questions 2

Block Difficulty:

Options:

is determined by the Ethereum Committee every fortnight to reflect the average amount of transaction and it cannot be influenced by the network itself.

increases when the time between mined blocks is below 10 seconds, while it decreases when the time is above 20 seconds.

increases when the time between mined blocks is below 20 seconds, while it decreases when the time is above 60 seconds.

Questions 3

In order to implement an ERC20 token contract, you'd need at least to implement the following functions and events in order to fulfill the interface requirements:

Options:

totalSupply(), balanceOf(address), allowance(address,address), transfer(address,uint256), approve(address,uint256), transferFrom(address,address,uint256). Events: Transfer(address,address,uint256), Approval(address,address,uint256)

name(), symbol(), totalSupply(), balanceOf(address), ownerOf(uint26),approve(address,uint256), takeOwnership(uint256),transfer(address,uint256),Events: Transfer(address,address,uint256), Approval(address,address,uint256)

Questions 4

The Fallback function:

Options:

cannot receive Ether, not even by adding the payable modifier.

can contain as much logic as you want, but it’s better to keep it short and not exceed the gas stipend of 2300 gas.

can be used to avoid receiving ether.

Questions 5

What are Ethereum Nodes?

Options:

Programs implementing the Ethereum Protocol to talk to each other and JSON-RPC interfaces to talk to the outside world.

A Java-Script library to compile and run Solidity Code.

A Framework for deploying and running smart contract in a decentralized way.

Questions 6

It's easy to write clean-room unit-tests with truffle:

Options:

for Java, JavaScript, and C++

for JavaScript using Web3.js

for Solidity and JavaScript

for any language, as long as it adheres to the open Testing-Interface from Truffle

Questions 7

Checking the balance of an address inside a loop of a smart contract constantly:

Options:

doesn't cost any gas.

cost gas every time we check the balance.

Questions 8

To store almost all data in the Ethereum Blockchain:

Options:

a Linked List with pointers to previous blocks hashes is used.

a Merkle Patricia Trie is used.

a Radix Trie is used because the Merkle Patricia Trie is too inefficient.

Questions 9

Externally Owned Accounts (EoA):

Options:

are changing their address every time a Transaction is sent because of the nonce.

are keeping their address, but on the blockchain a nonce is increased every time they send a transaction to avoid replay attacks.

Questions 10

Solidity files:

Options:

can't be split across multiple files, everything should be in one single file.

can be split across multiple files, but every contract must be in a file with the same name as the contract itself.

can be spread across multiple files. To import all contract from a file you can use "import 'myfile.sol'. To import Contract MyContract from myfile.sol you use "import {MyContract as SomeContract} from 'myfile.sol';".