The rivers will become dirtier and dirtier _______ we take action to protect them.
My friend Anne is a _______ girl, and she has a lot of imagination and new ideas.
—He’s never heard to sing a pop song so loudly, ______ he?—______. He is so shy.
We believe scientists will ______ a way to solve the problem of air pollution.
The window was broken. Try to ______ who has broken it.
—Did you take ______ one-day trip to the West Hill last Sunday?—Yes. It was fantastic! It’s _______ most delightful trip I’ve ever had.