The key word in Paragraph 4 is ______.

A．Brother and sister.
B．Unemployed young man and woman.
C．College students.
D．High school kids.

A．The bus tickets are cheaper than the train tickets.
B．The bus trip is comfortable because it is air-conditioned.
C．Bus stops at several cities along the way.
D．The traveler wants to experience another way of traveling.