At one time,there were long queues of people waiting outside the CAAC offices.中的waiting怎么用?
前面有个there were,是there be 句型么?后面的waiting是不是和前面的were构成过去进行时,感觉were被两个句型所用．是不是短一个were.自己瞎想．waiting在句中是个什么成分．
为什么要用waiting而不用wait呢？