问题
选择题
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
答案
答案：C
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。