he hurt his leg yesterday .He has difficulty walking now.句中为何walk用ing
题目
he hurt his leg yesterday .He has difficulty walking now.句中为何walk用ing
答案
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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举一反三
已知函数f（x）=x，g（x）=alnx，a∈R．若曲线y=f（x）与曲线y=g（x）相交，且在交点处有相同的切线，求a的值和该切线方程．
我想写一篇关于奥巴马的演讲的文章,写哪一篇好呢?为什么好
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