Cindy shut the door heavily and burst into tears. No one in the office knew _____ she was so angry.

Whitney Houston’s sudden death suggests that drug abuse is such a serious problem ___________ we should deal with properly.

No one but the experts in this field can _____ the difference between them. [ ]

Have you decided where to spend your summer holiday?—Not yet. We _________ go to Qingdao.

Faced with difficulties, you should believe your confidence is _______ makes a difference.