he hurt his leg yesterday .He has difficulty walking now.句中为何walk用ing

分类: 作业答案 • 2021-12-28 15:24:49

问题描述：

答

have difficulty (in) doing sth 在做某事方面有困难,省略了一个介词in,介词后的动词都是ing形式的,这是个固定搭配.
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