Which of the following is the role of Certification Authority (CA) in electronic commerce using public key encryption?

Which of the following is the role of Certification Authority (CA) in electronic commerce using public key encryption?

1. a) To manage a private key shared among the parties to the transaction.
2. b) To manage digital signatures of the parties to the transaction
3. c) To manage the passwords of the parties to the transaction
4. d) To issue a digital certificate for the public key of the parties to the transaction