30.some English-learning websites if you are free and you will learn a lot about how to s

问题补充：

30.some English-learning websites if you are free, and you will learn a lot about how to study English.

A. Having visited

B. To visit

C. Visiting

D. Visit

答案：

A. Having visited

B. To visit

C. Visiting

(答案→)D. Visit

解析：可联系答.案.网客服索取。