题干
It's very important ______ us ______ hard.
A：for; to study
B：of; to studying
C：for; studying
D：of; to study
答案(点此获取答案解析）
A
It's very important ______ us ______ hard.
A：for; to study
B：of; to studying
C：for; studying
D：of; to study
