Only by your attention what you are learning can you learn it well.
A. focus;on
B. pay;on
C. focusing;on
D. paying;on
网友回答
A. focus;on
B. pay;on
(答案→)C. focusing;on
D. paying;on
解析:by是介词,后面用动名词形式。句意:只有把精力集中在你所学的东西上,你才能学好它。focus...on...“把……集中在……上”,固定短语。