He speaks English well indeed, but of course not as a native speaker.
A. as fluent
B. more fluent
C. so fluently
D. much fluently
网友回答
A. as fluent
B. more fluent
(答案→)C. so fluently
D. much fluently
解析：not so\as ---as—“不如”；副词修饰动词。“他的英语确实很好，当然不如母语为英语的人说得流利。”所以答案为C。