从句其实本身就是一句句子,但是在一个长句中作为了一个成分的存在,所以需要一个词作为其本身与长句之间的连接.因此,只有连词可以引导.
比如时间状语从句：
When i was a child,I went to park with my parents every week.
He ran out of the room immediately as he heard the explosion.
比如地点状语从句：
He still stand at the place where she used to pass by.
More chairs have been set around the square (where) people always do the morning exercise.