Only by practising a few hours every day be able to play the piano well.
A. you would
B. would you
C. you will
D. will you
网友回答
A. you would
B. would you
C. you will
(答案→)D. will you
解析：考查倒装句和时态：句意：只有你每天练习几个小时，你才能把钢琴弹好。Only+副词/介词短语/状语从句+主句（主句用部分倒装），而且这句话的时间是every day，所以用一般现在时will，选D。