Which of the following is a true statement about blockchain?

A$)$ New blockchain records are bundled into blocks that are added to the chain one at a time.

B$)$ Each block of the blockchain is identified by an encrypted code called a hash and each biock also incluaies the hash of the previous block; the hash codes serve as links in the chain

C$)$ The network of computers continuously monitors the blockchain to ensure that all copies of the database are the same

D$)$ All of the above