这个是强调句,是强调句的特殊疑问句,是对疑问词进行强调.
判断是不是强调句的方法是:去掉It is ...that...后,句意及句子结构仍然完整的句子,就是强调句,
否则就不是.
特别提醒:去掉It is ...that...后,要把被强调部分还原到原来的位置上.
如问题中的句子去掉It is ...that...后,就成为:What makes them so unhappy?
结构及句意完整,因此What is it that makes them so unhappy?是强调句.
再如:It is a teacher that my mother is .
去掉It is ...that...后,如果不把a teacher 还原到它本来的位置,那么就成了:
A teacher my mother is .据此有人说,It is a teacher that my mother is .不是强调句.
这样理解就错了.因为应该把a teacher 还原到它本来的位置,即:My mother is a teacher.
所以,It is a teacher that my mother is .是强调句.
又如:It is exciting that we have succeeded in sending up Shenzhou V.
若将It is 及 that同时省去为：We have succeeded exciting in sending up Shenzhou V.
显然句子错误,因此,这个句子不是强调句型,而是主语从句.十分感谢！很明白！