选择正确的词语填空!
7、What doctors doubt is___ (whether;if) the little kid will recover from this serious disease or not.
8、Sue still doesn't remember___ (when;why) it was that she lost her wallet.
9、One reason I know___ (why;which) trade is a challenge is that best guesses must be well prepared in terms of incomplete information.
10、Jack was such a naughty boy ___ (that;who) we all thought he broke the vase.