A.must have seen B.can’t have seen C.needn’t have seen D.might have seen
单项选择题To protect the camera lens, be sure to reattach the lens cover（）returning the camera to its case.
A.when B.what C.whether D.why
单项选择题Before（）the envelope, please be sure you have enclosed all of the documents listed in your orientation packet.
A.sealing B.is sealed C.was sealed D.seal
