We should think about what we can do ____________ (keep) animals and plants from becoming endangered
题目
We should think about what we can do ____________ (keep) animals and plants from becoming endangered.
用所给动词的适当形式填空.答案是to keep,我想知道为什么加to啊?
答案
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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