Which level(s) must protect against both covert storage and covert timing channels?

Which level(s) must protect against both covert storage and covert timing channels?

A.
B3 and A1

B.
B2, B3 and A1

C.
A1

D.
B1, B2, B3 and A1

Explanation:
Reference: pg 302 Krutz: CISSP Prep Guide: Gold Edition