Mary keeps going to the English Corner,mainly _to improve_his spoken English
问题描述：
Mary keeps going to the English Corner,mainly _to improve_his spoken English
横线上的词做成什么成分,为什么不用 ing形式
答
to improve 动词不定式作目的状语目的状语前不是不能有逗号的吗这句前面不是有mainly 是动词不定式作目的状语对他所做的事的补充Mary keeps going to the English Corner that mainly to improve his spoken English 这句就不需要 逗号 ，这是一个从句