______ the ancient Egyptians built the pyramids puzzled people for centuries.

Many doctors and scientists are working hard on curing AIDS. We hope AIDS _____ one day.

I hear ________ students went to the hall to have the concert.

We can’t go home _____ the heavy rain and we have to wait _____it stops.[ ]

He knows a lot about films. No one in our class can ____________ him in that.