答案是A.that强调句。 但出题者没考虑到this morning是不能加介词的,出题者答案应该是D 另外给个例子: It was in 1949 that PR China was founded.强调句(去掉it was that成立) It was the year of 1949 when PR China was founded. (去掉it was when不成立) when引导状语从句,it指时间。(也有一说是when引导定语从句,修饰the year of 1949)本回答被提问者采纳