what did you have done this afternoon?和 what have you done at this afternoon?有什么区别?
题目
what did you have done this afternoon?和 what have you done at this afternoon?有什么区别?
答案
what did you have done this afternoon?的时态我认为是有问题的.因为它既不是完成时也不是过去时
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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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