There was thick haze（雾霾）in our city this spring. What do you think of it—I think __ cars we drive, __ pollution our city will have.

Excuse me!How long may I ________this book—For about a week.

Now more and more people have come to know the role that trees _____in our natural environment. [ ]

Shall we go hiking this Sunday–Sorry, I ___. I’ll have to take a piano lesson.

It is reported that two schools, ________ are being built in my hometown, will open next year.