Air is________and of no smell but we can feel its motion when there is a wind.
| A．unavoidable | B．unavailable | C．unaccessible | D．invisible |
He was deep in thought with his eyes_____ on the ceiling.
| A．fixed | B．fixing | C．fix | D．to be fixing |
The car was completely _____ and the driver seriously injured.
| A．broken off | B．taken off | C．written off | D．picked up |
Although the causes of cancer_____, we do not yet have any practical way to prevent it.
| A．are being uncovered | B．have been uncovering | C．are uncovering | D．have uncovered |
______run fast should take part in the 400-meter race tomorrow.
| A．Anyone who | B．Those who | C．No matter who | D．Whoever |
Was it in the factory_____ you worked five years ago___ you learned the technique?
| A．that; where | B．where; when | C．where; where | D．where; that |