As a matter of fact matters most in learning English is enough practice.A. where B. why

问题补充：

As a matter of fact, matters most in learning English is enough practice.

A. where

B. why

C. which

D. what

答案：

A. where

B. why

C. which

(答案→)D. what

解析：考察名词性从句的引导词。主语从句却主语，且意为：…的。故D正确。