It _____ last week that the haze(雾霾)in Beijing caused many problems.

He had to pause from time to time to wipe the sweat from his forehead, because the air-conditioning system _________.

The boy ______ blue trousers______.

Where have you been recently?—I ______ in Hangzhou on business for a week last month.[ ]

The sign near the river _________ “Don’t swim in the river.”