—We're doing a lot to protect our environment, but it is not good enough. —So we should try______ to look after it.
The plane for Yunnan will______ in two hours. Let’s go to the airport as soon as possible.
I’m going to the beach _______ bus with my family this summer.
Oh, my God! I can ______ put on my trousers. I must be getting heavier.
—Could I invite my friends to my birthday party?—Sorry, you ______.
Our math teacher is very kind ______ he looks very serious.