I had a little trouble in English grammar.A. learnB. learnedC. learningD. to learn

问题补充：

I had a little trouble in English grammar.

A. learn

B. learned

C. learning

D. to learn

答案：

A. learn

B. learned

(答案→)C. learning

D. to learn

解析：句意：我在学英语语法方面有点小麻烦。本句中in是介词，后面接名词或者动名词作宾语，故选C。