Which of the following statements is true?
(a) In blockchains, any change or new transactions can be realized only by adding a new block of information to the historical transaction records.
(b) In blockchains, one doesn't erase or override the past records, it adds transactions in a chronological order to a growing list.
(c) Unlike the ledgers maintained by banks, Bitcoin's blockchain is replicated on networked machines around the world; hence it is called a "Distributed Ledger".
(d) All of the above.