necessary for us English well.A.It’s; to learnB.It’s; learn C.That’s; learn

问题补充：

necessary for us English well.

A.It’s; to learnB.It’s; learn C.That’s; learn

答案：

解析：固定句式It’s adj for sb to do sth，做某事对于某人来说怎么样。故选A。