【单选题】

{{I}}Questions 18 - 21 are based on the following passage about Walkman.{{/I}} Why there are signs" Keep Your Personal Walkman Personal" in London’s underground

A、Wakman is prohibited to take on the UndergrounD、
B．Listening Walkman may disturb other passengers.
C．Passengers should watch out their Walkman.
D．Listening Watkman is one’s private thing and cannot be disturbed by others.