我背疼,到底是用I had a sore back还是 I have a sore back.
题目
我背疼,到底是用I had a sore back还是 I have a sore back.
答案
如果现在不痛了,你就说 I had a sore back.现在痛,就说 I have a sore back.
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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