This year the number of the US students in China has increased by 18.4percent compared to

问题补充：

This year the number of the US students in China has increased by 18.4percent compared to last year.

Ato study

Bstudying

Chaving studied

Dstudied

答案：

A. to study

(答案→)B. studying

C. having studied

D. studied

解析：考察分词用法。本题考察的是分词短语作定语的用法。Students与study构成主动关系，使用现在分词的形式表示主动。Studying in China修饰students。指在中国学校的美国学生。句意：与去年相比，今年在中国学习的美国学生的数量已经增加了百分之18.4.故B正确。