He visited three cities when he stayed in the U.S.,____New York, Washington and Houston.

A. such as　　　　　 B. they are　　　 C. which is　　　　 D. that is

He visited three cities when he stayed in the U．S．, ________ New York, Washington and Houston．

1. A.
   such as
2. B.
   they are
3. C.
   which is
4. D.
   that is