One of the difficulties we have English is how to remember new words and expressions.A. to

问题补充：

One of the difficulties we have English is how to remember new words and expressions.

A. to learn

B. in learning

C. learn

D. learned

答案：

A. to learn

(答案→)B. in learning

C. learn

D. learned

解析：原句意思是：我们学英语时的一个困难是如何记住单词和短语.have difficulty in doing something的意思是“做某事有困难”。根据句意,可知选B.