Question

请教sat语法问题

Had it not been for two particularly skillful members of the work crew, we could
not have completed the apartment renovations on schedule.

答案说这句话正确，可是我不明白“Had it not ”“have completed”为什么要用完成式，
怎么理解呢？

Answer 1

1.这是虚拟语气当中的一种情况
If it had not been for sth. , sb. could/ would not have done sth.
前面是过去完成时 had not been ,后面是现在完成时 have done
这是这种用法的特点

这句话是表示 如果没有了sth. 的帮助， sb。将不可能完成某事

那么把最开始那种结构套到本题中，就是
If it had not been for two particularly skillful members of the work crew, we could
not have completed the apartment renovations on schedule.
如果没有了……的帮助，我们将不能按时完成

2. 而这题还涉及到另一个知识点
if it had not been 可以变成 had it not been
if it should not been 可以变成 should it not been
if it were not been 可以变成 were it not been

这是虚拟语气中的特殊用法，都是把if省掉，然后it后面的助动词提到前面来，表示如果不是……的话

正如你这题，本来是If it had not been for ，现在就变成了had it not been for， 其实两个都是OK的~

Answer 2

这个句子是个虚拟语气，表示与过去事实相反，从句用过去完成时，主句用情态动词的过去式+have +过去分词。表示：要不是……，……事就不可能发生。这句话的意思是：要不是工作团队中两个技术特别过硬的成员的话，我们就不能按时完成房间的修缮工作。