Questions 17-20 are based on the following talk about tidal wave. According to the passage, what causes tidal waves

A．To cover the rear wheel of the car with bees.
B．To call a local beekeeper to deal with the situation.
C．To put the queen bee and her followers in a barge box.
D．To hide a passenger in the rear part of the car.

A．densely-populated cities surrounded by nearly-empty countryside.
B．overpopulation being real.
C．an undesirable situation resulting from there being too many people,
D．all the above.