作用
1． 作状语
1) 表示时间 如：
Her homework done (=After her homework was done),Lucy decided to go shopping.
2) 表示原因 如：
There being no buses (Because there were no buses),we had to walk home.
3) 表示条件 如：
Weather permitting (If weather permits), we will go to play football.
4) 表示方式或伴随 如：
He rushed into the room, his face covered with sweat.
2． 作同位语 如：
There are two doors, one leading to the bedroom, the other (leading) to the kitchen.
