_____by the police,the kidnappers had no choice but to surrender

问题描述:

_____by the police,the kidnappers had no choice but to surrender
为什么选surrounded 怎么看出被动的?还是有什么其他原因?
最后的to surrender 是no choice的固定搭配?我怎么记得是but do

选surrounded 是因为kidnapper是被警察包围,并且从“by”也可以看出来应该用surrounded
固定搭配,have no choice but to do sth