—What did you do during your summer holiday?—I spent my holiday English in summer classes

问题补充：

—What did you do during your summer holiday?

—I spent my holiday English in summer classes.

A. improving B. improves C. to improve

答案：

解析：句意：暑假你都做什么了？我花费整个暑假都在上补习班来提高英语。spend sth ( in ) doing sth花费时间或金钱做某事，固定句型，故选A