在地面，将机翼防冰按钮置于ON位时会发生什么情况？（）
A.机翼防冰活门打开30秒，然后关闭
B.机翼防冰活门不打开
C.机翼防冰活门保持打开
参考答案：A
The scientist made several discoveries, _______. [ ]
A. which we think are important
B. which we think that is important
C. we think which are important
D. which we think is important
She learns something _____ art and history on Sundays.[ ]
A. in
B. of
C. for
D. about
