A ruler is 2 dollars and a pen is 3 dollars. How much are they —They are ________.

Professor James will give us a lecture on the Western culture, but when and where ________ yet.[ ]

I soon found that the work I was doing had already been done by someone else－, I was wasting my time.

While _______ across the street, you should be careful.[ ]

This camera is of good quality. If it ______ break down within the first year, we would repair it at our expense.