1、it remains_to be seen_wether the operation was successful
为什么不用to see而用to be seen。
2、i'm sorry,sir. Your record isn't ready yet. It_is being repaid_in the
factory.
为什么不用has been repaired。
3、All americans would remrmber April 14,1865,_when_Abraham Lincoln was shot
that night after a very busy day,the president and his wife to Ford's
theatre……
第一个为什么不用As。
4、lincoln, one of the greatest American presidents,was shot and_died_early
the next morning.
为什么用died，不用had died，林肯又不是在被枪击后立刻死亡的。
5、he look around carefully so as to find the guards who were pritecting from
the enemy.To his joym,there was none of_them_and nobody noticed him.
为什么用them不用guards.
第三个题我是说那个空为什么不用As
remain这个词比较重要，他有两个用法。其一是联系动词表示“保持”，用法是remain<adj>/<n>
其二是实意动词，表示“留待“用法是remain to be done
e.g.It remains to be seen whether the medicine is the best cure for cancer.
2.因为提示'isn't ready yet'说明没有完成，动作正在持续，怎么能用现完呢？
3.填空考的是非限定从相信你能看得出来。定从的题解题思路都是一样的，先看从句缺成分吗，不缺选一个关系副词,缺就选关系代词。想这句话从句不缺成分那么先行词就只能是那个日期，选一个关系副词在句中做时间状语。你用as的话，它指代的名词在从句中还能做什么成分呢？
4.and连接的两个动词时态必然一致。还有我觉得你对时态的理解有点问题。过完强调动作的先后关系，具体来讲是die在shot前面发生。过去时就是说动作发生在过去，不强调动作的先后。
5.of+范围,你用guards必须加上冠词the特指，告诉读者在”这样的“范围以内，这是英文的潜规则
有问题请追问，您的采纳是我的动力~