（ ） the door slowly opened , there was a hysterical scream of terror.
A.when B.while C.as D.whenever
PS:正确选择是B。解释是说有同时性和暂时性。表示很不明白，为什么不可以选A呢。而且看起来其他选项也没有什么不合适的呢。
The book （ ）was not in the school library.
A.which the professor referred us
B.which the professor referred to us
C.to which the professor referred to us
D.to which the professor referred us
PS:正确答案是D。解释说因为固定搭配refer sth to sb.那么TO的宾语应该是人才对啊，用D不就把宾语变成书了吗。