Listen ! Helen is singing in the next room.—It _______ be Helen. She has gone to Beijing.

My aunt and uncle usually bring some gifts ______ me when they come to visit.[ ]

Standing on the top of the hill, you will get a better _______ of the whole city.

After Yang Li wei succeeded in circling the earth, _____ our astronauts desire to do is walking in space.

The rivers will become dirtier and dirtier ______ wetake action to protect them.