Is ____ necessary to complete the design before National Day?
Mary answered all the questions __________the last one, which she had never heard of before.
I've worked with children before, so I know what__________ in my new job.
Get down to the experiment right away if possible,__________ you will not finish it before dark.
---What do you think made Mary so upset?--- ______ her new bike.
Mr Reed made up his mind to devote all he had to______ some schools for poor children.