【单选题】

Questions 14 to 17 are based on the following passage.At the end of the passage, you will be given 20 seconds to answer the questions.

Now listen to the passage.
Which of the following statements is NOT true of the exhaust systemA．It regulates the speed of a car.
B．It channels out the waste products of combustion.
C．It reduces the noises generated by the engine.
D．It cleans up the emissions harmful to the environment.