问题补充：
单选题Shelookssad.Couldyoupleasetellme____thatpreventsherfrombeingashappyasbefore?A.what it isB.it is whatC.how it isD.it is how
答案：
A解析主要测试宾语从句。只不过把宾语从句的测试放到强调句型中来测试，首先按照强调句型的判断方法：把It is···that去掉，则很容易地看出what引导的宾语从句，而且what在从句prevents her from being as happy as before中充当主语。所以选择A最佳。译文：她看起来不高兴。你能告诉我究竟是什么让她没有以前那么高兴了吗？
