We can never expect ________ bluer sky unless we create ________ less polluted world.(2009·安徽)
how to do the homework, I went to ask my teacher for help.
You’d better leave the windows _________ and the door ___________.
We should spend as much time as we _______ over our lessons.
It’s _______ much more than I ________ it.
She looked unhappy because she had made ________ mistakes in the English test.