In the process of bitcoin mining, which of the following statement is correct?

A. A blockchain is built every 40 minutes and a reward of bitcoin is given to the winner bitcoin miner

B. A blockchain is expressed in a series of 256 bits, which can be decrypted into an information package that contains bitcoin transactions and associated accounts

C. The winning bitcoin miner only needs to solve the first N bit digits of the blockchain, designated by the system and does nothing else

D. The reward for the bitcoin winner is 50 bitcoins in perpetuity