It is very important for us English well.A. learnB. learningC. to learnD. learned

问题补充：

It is very important for us English well.

A. learn

B. learning

C. to learn

D. learned

答案：

A. learn

B. learning

(答案→)C. to learn

D. learned

解析：本题中的it是形式主语，真正的主语位于句尾，用动词不定式to do，故选C。