Which of the following statements about blockchain is not true?

Select one:

a$.$ The records in a blockchain are secured through cryptography

b$.$ Blockchain is especially suitable for environments with high security requirements and mutually unknown actors.

c$.$ Once recorded, a blockchain transaction cannot be changed

d$.$ The data represented in a blockchain is maintained in a central database

e$.$ Each block in a blockchain is connected to all the blocks before and after it$.$