Question

The research mainly deals with the difficulty the students have ______ their

attention on their study all thetime.
A. tofocus B.to be focused C. focusing D. focused
答案是C，为什么

Answer 1

the students have是前面省略了that的定语从句，修饰the difficulty 的，去掉不看，就是：
The research mainly deals with the difficulty focusing attention on their study all thetime
difficulty和focus是主动关系，用现在分词

这份研究主要是解决学生们在学习中（能否）专心的困难

Answer 2

其实用到一个短语 have difficulty/trouble doing sth
这道题目中将the difficulty 提前 ，后面 the students 到后面都是修饰的