英语语法分析

After police cordoned off the road, frustrated and alarmed drivers looked on until vets managed to tranquillise the animal. Police then shot it dead.

警方用警戒线围起了公路，受阻的司机们只能等待观望，直到赶来的兽医设法使动物安静下来，于是警方射杀了这只公牛。