1.it is reported that the president once ___ in the Viet Nam's war for three years from 1966-1970.A served B had severed 2.i wasn't paying attention to what he was talking about ,so i am afraid i __ his speech very well .A did not understand B has no

1.it is reported that the president once ___ in the Viet Nam's war for three years from 1966-1970.A served B had severed 2.i wasn't paying attention to what he was talking about ,so i am afraid i __ his speech very well .A did not understand B has no
1.it is reported that the president once ___ in the Viet Nam's war for three years from 1966-1970.A served B had severed 2.i wasn't paying attention to what he was talking about ,so i am afraid i __ his speech very well .A did not understand B has not understood .3.i___ good at table tennis ,but i haven't played it for ages.A am b was 4.the party was successful,but we thought it a pity not ____ you .A to have invited B inviting 5.--if Mary doesn't come to work on time,she may be fired .--Surely sheis not so foolish ____it .A as not to realize B as not realizing 6.A number of new machines were installed in the factory ,thus ___ an increase in production .A resulting in B results 7.All the managers agreed that the matter required____ .A looking into B to be looked into

1.it is reported that the president once ___ in the Viet Nam's war for three years from 1966-1970.A served B had severed 2.i wasn't paying attention to what he was talking about ,so i am afraid i __ his speech very well .A did not understand B has no
1A
因为reported,once等关键词强调,有一次,强调过去一段时间内发生的事情
作为总统,可以确定他现在不在越南,更不可能亲自打仗（除非上下文交代）
A要比B好
那么他们的强调点,我认为是
the president once worked in the Viet Nam's war for three years
（现在不在越南了）
the president has worked in the Viet Nam's war for three years
（现在还在越南）
the president had worked in the Viet Nam's war for three years
（现在在不在越南不清楚）
2A
文字游戏
这里是强调过去的一段时间——我处于不明白状态
但不代表带现在为止（用has完成时）我还不明白,因为 wasn't表示我那段时间不集中精神,am 表示此刻我回忆那时的情景我不明白（至于到底现在明不明白没说）
用了现在完成时,表示到现在为止我还是不明白（但事实上面分析了）
ok?
3A
文字游戏
我是乒乓高手,但我几年没玩了
but表示过去对于现在的转折（过去：到现在几年没玩.现在的状态：我认为我是高手,只要我认为就行,上下文又没强调事实）
如果用was,那就去掉but
4A
was表示事实party已经开完,后面这句话是虚拟,本应邀请你,却没有
it （is）adj to do句型啊,当然这里换成了名词,一样
5A
如此,以至于,相当于,so..that（只不过加句子）
so..as to
词组
6A
也是词组,导致（一个结果）,单独的result根本没意思啊
result from表示由……导致
常用词组
7A
要么加doing,要么
但我require 应该没有to be done 的形式,可以问一下老师吗
我觉得是这样
只有7题有疑问,可以交流吗?hi交流好了