Questions 18 to 20 are based on a short talk about bus. You now have 15 seconds to read Questions 18 to 20.

What is "bus bunching"

A．The phenominon that a number of buses arrive at a stop simultaneously.
B．The phenominon that a number of buses are delayed at the same time.
C．The phenominon that a number of buses are running on the same street at the same time.
D．The situation that a bus has more than the usual number of passengers on board.