单项选择题

Questions 17 ~ 20 are based on a monologue by a tour guide giving some information about the BART system. You now have 20 seconds to read Questions 17 ~ 20.
What kind of people don’t need a ticket

A.A group of 4 children.
B.Children not more than 4 years old.
C.Those who ride every day.
D.Those who are free from work.