___is very important___us__a foreign language.A.It;for;to learn B.That;for;to learn原因
问题描述：
___is very important___us__a foreign language.A.It;for;to learn B.That;for;to learn
原因
答
选A，That必须指代一个之前提到过的东西，It在这里做形式主语。
答
A，It is adj. for sb. to do sth.
是固定句型
答
A
答
A it is +adj +for sb +to do 句式
答
A 固定句型 it is +adj for sb to do sth