英语语法疑问

英语语法疑问
It is high time +一般过去时,作为虚拟语气.
那么,it was high time 后面用一般过去时还是过去完成时?
It was the training that he had as a young man () made him such a good engineer.
A has
B later
C that
D which
我选B.
因为这是强调句型,如果不强调：
The training he had as a young man made him such a good engineer已经是一个完整的句子了,所以,不应该用连词that或which来引导.为什么?
我忽然明白了，应该选C that
这个C才是和前面的it was组成强调句型。
前面的that引导的是定语从句。
另外，我前面的那个问题：it was high time that 后面动词应该怎么用？用什么时态？