Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 31 to 35.           Sometimes mail arrives at t

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 31 to 35.

          Sometimes mail arrives at the post office, and it is impossible to deliver the mail. Perhaps there
is an inadequate or illegible address and no return address. The post office cannot just throw this
mail away, so this becomes "dead mail." This "dead mail" is sent to one of the U.S. Postal Service's
dead mail offices in Atlanta, New York, Philadelphia, St. Paul, or San Francisco. Seventy-five million
pieces of mail can end up in the dead mail office in one year.
              The staff of the dead mail offices have a variety of ways to deal with all of these pieces of dead
mail. First of all, they look for clues that can help them deliver the mail; they open packages in the
hope that something inside will show where the package came from or is going to. Dead mail will also
be listed on a computer so that people can call in and check to see if a missing item is there.
          However, all of this mail cannot simply be stored forever; there is just too much of it. When a lot
of dead mail has piled up, the dead mail offices hold public auctions. Every three months, the public
is invited in and bins containing items found in dead mail packages are sold to the highest bidder

The word “they” in paragraph 2 refers to______.