Which of the following are among the reasons why a blockchain is immutable?

A.Each block contains the hash of the header of the previous block

B.Each block header contains the Merkle root corresponding to all included transactions

C.Recreating valid block hashes for changed data is relatively easy and fast, allowing for modifications to past records to be immediately accepted and validated

D.Transactions in a block can be easily changed without altering the overall Merkle root for that block