all the cash crop —— before we placed an order.
题目
all the cash crop —— before we placed an order.
A.is exported B.has been exported
C.will be exported D.has been exported
和关于这方面的知识点,感觉很多单选都是这样的好多“has been had been”不懂
D是had been exported
答案
has been是现在完成时,如果前一个动作是现在时,那么应该用现在完成时.
例:I go to Beijing.
I have been to Bejing.
had been是过去完成时,如果前一个动作是过去时,那么应该用过去完成时.
例:I went to Beijing.
I had been to Beijing.
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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