While he ________ his homework , his mother came in.

Stay away from junk food, please. It’s bad for us，_________ for children!

.____me that you choose,so long as you finish the job on time.

The MP4 player _______was bought yesterday isn’t working now. It needs to be repaired.[ ]

When ______ comes to research into heart disease and its effects on the body, we do not have adequate substitutes for the use of animals.