—Do you still remember the days ______ we spent in the countryside ten years ago?
—Yes，I'll never forget the experience.
| A．that | B．when | C．on which | D．what |
It was very important for us ________ happy every day.
| A．to stay | B．stay | C．stayed | D．staying |
-You look upset.
-Yes, this is the first time I________ form home.
| A．leave | B．left | C．have been away | D．is away |
The police________ already_______ his house but haven’t found any evidence against him.
| A．has; searched | B．have; searched | C．has; searched for | D．have; searched for |
We should consider the students’ request________ the school library should provide more books on popular science.
| A．that | B．when | C．which | D．where |
He was heard________ three songs in the next room.
| A．sing | B．to sing | C．singing | D．sung |