(2013·重庆卷)Recycling is one way to protect the environment; reusing is ______.
Why many adolescents have trouble communicating with their parents lies in _______we call “generation gap .”
I _______less than a pound a week when I first started work .
_______the cost ,the project will take a lot of time as well .
These professors had interrupted their own research to accept an invitation to _______in an unusual experiment .
I really don’t know why he hates everything we _______.