​the stone on the river bank rolled under her feetshe was()into the river,and she called out for help.答案给的是being pulled,pulled为什么不行.没有强调正在进行而且后面也是called不是was calling.如果被拉下去这个

​the stone on the river bank rolled under her feetshe was()into the river,and she called out for help.答案给的是being pulled,pulled为什么不行.没有强调正在进行而且后面也是called不是was calling.如果被拉下去这个
​the stone on the river bank rolled under her feet
she was()into the river,and she called out for help.答案给的是being pulled,pulled为什么不行.没有强调正在进行而且后面也是called不是was calling.如果被拉下去这个动作是过去进行,那呼救应该也是同时发生

​the stone on the river bank rolled under her feetshe was()into the river,and she called out for help.答案给的是being pulled,pulled为什么不行.没有强调正在进行而且后面也是called不是was calling.如果被拉下去这个
她是被拉下河流的所以用be+done的形式,因为中间有and做连接词,前后主语一致,后句可省掉be动词.表示动作同时发生,又因为前面句子的be动词是was,所以后面句子省去了谓语was.完整句子：she was being pulled into the river,she was calling out for help.所以前面句子用过去进行时的被动语态就是was being done,

pulled当然可以，用being pulled增加了生动性。