It is know to all that it takes years of ( )practice to gain the skill of( )expert.
问题描述：
It is know to all that it takes years of ( )practice to gain the skill of( )expert.
Aa;the
B/;an
Ca;an
D/;a
答
B.
years of practise(practise不可数）类似的years of hard work
expert原因开头加a.