They had to spend the cold night___to a tree.
a. tying b.in tying C. tied D. be tied

In the office I never seem to have time until after5:30 p.m., __ many people have got home.
A. whose time B. that C. on which D. by which time

___many times, she still couldn*t understand it.
A. told B. Having told C.She was told
D. Though being told

The headmaster often comes into our class to__ our difficulties.
A. look at B. look into C. look for D. look up

The shop will be closed during __.
A. repair B. a repair C. repairs D. repairing

请英语高手详细说明为什么，谢谢

1.答案选c.这个题目考察非谓语动词作方式状语.因为出现spend ,所以会想到spend some time in doing这个结构，但是用于这个结构的动词必须能持续一段时间，因为是花一段时间做某事，例如：spend one hour (in )writing,因为write写 这个动词可以持续一段时间，所以可以用这个结构，但是tie绑这个动词不能持续，因为绑这个动作不能延续，但是绑着的这种状况可以持续。所以不符合spend..in doing,因为绑着的这个状态可以持续，所以可以用方式状语，因为人是被绑着的，所以用过去分词tied，这个句子的意思：他们被绑在树上，度过了一个冰冷的晚上。做这样的题目，一定要好好分析动词和句子结构。不能被spend..doing这种惯性思维所左右
2.答案选d,这个句子考察非限定性定语从句，因为后边的句子用的是many people have got home.因为使用了完成时态，所以要选by引导的时间状语，所以选择by which time
3.答案选A
因为是他被告诉了很多次，但是他仍然不理解它，对于SHE来说，是被告诉，所以应该选被动told,如果选she was told many times 的话，就变成了两个句子，这样的话，两个句子之间应该有连词and,因为原题中没有连词，所以选项c排除， 选项b是主动式，所以也排除，选项d虽然是被动，但是being told 表示正在进行的动作，而many times 表示完成时态，所以也排除
4.答案选b
look at:看见；look into: 调查或者观察某事物；look for:期盼或者期待某事物
look up:抬头看
5.答案选c repairs:修理，修补，一般用复数形式。例如：
The shop is closed for repairs