---I’ve told her many times, and she still forgot about it!---I understand. It’s true that

---I’ve told her many times, and she still forgot about it!
---I understand. It’s true that she be very forgetful sometimes.
A. can
B. should
C. ought to
D. must

(答案→)A. canB. shouldC. ought toD. must解析：考查情态动词。can 可能，表示理论上的可能性；should，ought to应该；must必须，一定。It’s true that she be very forgetful sometimes表示她有时可能真的比较健忘。表示理论上的可能性。所以选A。

这下我知道了