Which of the following statement(s) is/are false: a. Because block chain is immutable, it is impossible for cryptocurrency exchanges to commit fraud or another consumer to steal and spend the cryptocurrency of another consumer.

b. Consensus computing is a network of computers working collaboratively to make sure information and transactions are verified. c. Blockchain is a transaction record. It is a database of all of the transactions associated with a function d. In order to use your Bitcoin you have to have a public key that you can share with someone, and a private key that you keep to yourself.