What Have Researchers Found Regarding Failure of Long-Term Memory

What have researchers found regarding failure of long-term memory

A)  The mere passage of time is the sole cause of forgetting. 
B)  The passage of time is not as influential for forgetting as what happens during the retention interval. 
C)  Subjects who sleep during the retention interval forget more than those who remain awake. 
D)  The passage of time is critical for forgetting semantic information, but not for episodic information.