Questions 19 to 21 are based on the passage you have just heard.

A. To produce a gas containing carbon and hydrogen.
B. To remove impurities from methanol.
C. To heat the reactors.
D. To prevent dangerous gases from forming.

A. The man has mistakenly received someone else’s books.
B. The man changed his major from art to business.
C. The man recently moved off campus.
D. There are two students named Robert Smith.