Which of the following would be the BEST reason for certificate expiration?

Which of the following would be the BEST reason for certificate expiration?

A.
To keep the server from using the same key for two sessions.

B.
Brute force techniques are likely to break the key if given enough time.

C.
Renewal keeps the log files from getting too large.

D.
The longer an encryption key is used the more processing power it will consume.