Who helped you repair your bike?—________ ! I repaired it all by myself.

Betty stayed at home and studied_____ exams last weekend.[ ]

I can’t connect my computer to the Intemet. There must be ______ wrong with it.

My father _________ Beijing on business for three days. He will be back in two days.

Now China is fighting against illegal cooking oil（地沟油）, a kind of waste oil _____can cause a lot of illness.