They were so busy talking with each other that they forgot the time怎么解释?
题目
They were so busy talking with each other that they forgot the time怎么解释?
为什么so后面是动词的ing形式啊?
答案
这里用了固定短语 be busy doing sth 忙于做某事
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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