Alfred Points an Unloaded Gun at Buster and Threatens to Shoot

Alfred points an unloaded gun at Buster and threatens to shoot. Unobserved by Alfred , Cassie, who is Buster's wife, witnesses the threat and believes Alfred 's gun is loaded and that Buster is about to die. Cassie pulls out a gun and shoots and kills Alfred. In this case:

A) Cassie cannot successfully invoke the privilege of defense of others because Alfred 's gun was unloaded.
B) Cassie can successfully invoke the privilege of defense of others because of her reasonable belief at the time she shot Alfred .
C) Cassie  is liable because one can use deadly force only to protect herself.
D) Cassie was entrapped into believing her husband was about to be killed, so she has a valid defense.