People should open the window in the morning to make air ______ in order to keep the indoor air fresh.
| A．spread |
| B．remove |
| C．float |
| D．circulate |
Scientists are convinced _______the positive effect of laughter ______ physical and mental health.
| A．of ; at | B．by ; in | C．of ; on | D．on ; at |
Many of them turned a deaf ear to his advice, ________ they knew it to be valuable.
| A．as if | B．now that | C．even though | D．so that |
It is so difficult a question_______ none of the kids could work it out.
| A．as | B．that | C．which | D．X |
Kunming is called“Spring City”, but it _____ snow in winter.
| A．shall | B．can | C．must | D．might |
The old black woman sat under the pine tree, her grandsons, ______ around her, ______ to an old story.
| A．seating; listening | B．seated; listened | C．seating; listened | D．seated; listening |