885-01-23

23.   In 1980 the United States exported twice as much of its national output of goods as they had in 1970.

(A) twice as much of its national output of goods as they had

(B) double the amount of their national output of goods as they did

(C) twice as much of its national output of goods as it did

(D) double the amount of its national output of goods as it has（C）

(E) twice as much of their national output of goods as they had

请教两个问题 1, 这里A中的had 能否认为是had exported 的省略形式?

                      2, 1970 年的动作发生在1980年之前, 为什么不需要用过去完成时?

我对于一般时态和完成时态的选用总是很糊涂, 想得头痛, 多谢指点!                    

多谢楼上两位指点!

但是我还是不太明白:      

horsefish说: 完成时是过去的过去, 发生的事要对第一个过去有影响才用完成时.  ------ 就是说前面的事对后面的事有影响,对吧? 可 怎么就叫有影响, 怎么样就没影响呢?

   scots 说 "in two decades"，这是一个现在完成时的时间标志。------- 可是 那原文用during, 不要求一定用完成时啊.

情况longman 对during 的解释:

1
from the beginning to the end of a period of time
During the summer she worked as a lifeguard. He slept calmly during the early part of the night. Foxes remain hidden during the day.
2
at some point in a period of time
My father was killed during the war.

I mentioned the subject during our discussions at her Washington office.

你可以试着把后面的句子补全试试，即：句子应为In 1980 the United States exported twice as much of its national output of goods as they had exported in 1970呢，还是应为In 1980 the United States exported twice as much of its national output of goods as they exported in 1970呢？

我想很明白，这里有明显的时间点表示动作发生在过去，所以应该是过去时才对。

好像有道理. 但是我有点似懂非懂, 得去找些用过去完成时的例子对比一下, 哪位对时态尤其是过去时和过去完成时的区别比较清楚的 朋友劳驾给详细讲讲, 谢谢了!