The time she has devoted in the past decade ______ the disabled is now considered to be very valuable.
There is no doubt ____ John will come by bus.
Before you leave the lab, the doors and windows ____shut in case of rain.
Did John ____ the general cleaning yesterday afternoon?
To enjoy the scenery, Irene would rather spend long hours on the train ___travel by air.
For some students, the computer serves only _____ a tool that is used to play games.