--- What ____ have happened to Kevin? --- He might have run into some trouble. 

Whale beachings（搁浅）_______ be caused by factors such as illness, or disorientation（迷失方向）caused by extra noise in the oceans, ______ shipping or oil and gas drilling.

The manager commanded that the work ____ finished by the end of this month. 

One of our rules is that every student ______wear school uniform while at school.

—The research on the new flu virus vaccine is challenging and demanding. Who do you think can do the job?     —______ my students have a try?