1. They hurried away when a man they said was plainclothes security began taking photos of the conversation.
当一名据他们说是便衣安全人员的男子开始对谈话人拍照时，他们匆匆告辞了。
2. The young man wandering on the street acted so suspiciously that the policeman in plainclothes brought him to the police station.
这个在街上闲逛的年轻人行迹十分可疑，以至于便衣警察将他送到了警察局。
3. The plainclothes officers were told to keep the suspected man under constant observation.
便衣警察受命不断监视那个有嫌疑的人。
4. Many of these first immigrants opened clothes-cleaning businesses and low-cost eating places. The plainclothes officers were told to keep the suspected man under constant observation.
他们中的多数人开办了洗衣店和便宜小吃铺。便衣警察受命不断监视那个有嫌疑的人。