as is often the case 和 as often happens
问题描述：
as is often the case 和 as often happens
为什么第一个中要加is而第二个不用呢?
答
一句话只能有一个动词,不能有两个动词啊,happen已经是动词了,所以就不能加is了,前面的一句要是去掉is就没有动词了