Question

had electronic computers not been invented

虚拟语气
Had electronic computers not being invented,many problems of space flight _____ now.
(A) would not have been solved
(B) would not be solved
(C) must not be solved
(D) should not have been solved
if the United States had built more homes for poor people in 1995,the housing problems now in some parts of this country____
so serious.
A.wouldn't be B.will not have been
C.wouldn't have been D.would have not been.
两个题目的区别.

Answer 1

A A
第一题的意思是,如果不是计算机的发明,很多问题到现在都还没有办法解决.
用时间点来表示：
-------计算机发明-------问题解决----------现在-------
（过去的过去） （过去）
第二题的意思是,如果美国在1995年就给穷人造一些房子,现在在许多地方的居住问题就不会那么严重.
用时间点来表示：
-------1995年建房子-------住房问题-----------------
（过去） （现在）
可以看出,第一题中的假设是对过去的过去的假设,第二句的假设是对现在的过去的假设.