—Your English is really good. How do you learn English?— watching English movies.A. With B

问题补充：

—Your English is really good. How do you learn English?

— watching English movies.

A. With B. By C. At

答案：

解析：句意：你的英语真的很好，你是如何学习英语的？通过看英文电影。介词by表示通过什么方式，后接动词的ing形式，故选B。