Some people are worrying about the possibility ________ mobile phones could be responsible for a range of illnesses, from rashes(皮疹) to brain tumors．

I am very glad that our class_____ in taking the first place in the singing competition. —Congratulations!

Is your math book on the desk, Tommy?—No, it isn’t. It’s _______.[ ]

The Great wall is knownthe world.

Yesterday, I saw _________ enjoy _________ in the park.