【河北省2015年中考英语试题】 This food is free. You don't have to _________ it.
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.
This isn’t my sister’s skirt. ______ is blue.
Now the air in our city is ______ than it used to be. Something must be done to stop it.