1. The scientists wanted to keep people ( B ) about the breakthrough in their experiment.

A. inform B. informed

C. informing D. to inform

根据 keep people 可知后面必然是inform的-ed或-ing形式，进一步说 people 与 inform 的关系是people 被 inform，所以是 informed。如果这个不清楚，可以根据词意选择，要选的词可以理解成必须是一个形容词，那么 informed 的是一常见形容词，意思是“见多识广的，有见识的”；而informing 并非一固定常见词。

2.When I first arrived in Japan, I was surprised （ D ） the way people greeted each other.

A. of B. to

C. with D. at

选择 D，固定搭配 （fixed collocation）即 be surprised at something / sb......

3. Not until that day （ D ）the importance of good manners in a job interview.

A. did I realize B. I did realize

C. I have realized D. have I realized

选 D，将此题的句子还原就是：

I have not realized the importance of good manners in a job interview until that day.

同时 not until 在句首时要求部分倒装。

4. The market economy is quickly changing people’s idea on （ C ） is accepted.

A. that B. which

C. what D. how

选 C