It is only by practising English for several hours every day be able to use it freely.
A. will you
B. may you
C. that you will
D. when you must
网友回答
A. will you
B. may you
(答案→)C. that you will
D. when you must
解析：考查强调句型。强调的是方式状语，不被强调的部分应用that引导。
【标签】强调结构