We work together to achieve our common purpose: ________ world that is safer, cleaner and healthier than ________ one we are living in.
To make our city greener and cleaner, we need ______ trees.
–Why didn’t you answer my phone last night? –I ______ on my way home.
He is always making ______ for his being late ______ school.
______ you have nothing important to do, why not come with me to the cinema?
I think ______ necessary ______ to take more exercise.