Questions 17 to 20 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. All of the following are true according to the passage EXCEPT ______.
A．in the wartime trained message pigeons can fly 500 to 600 miles B．hardships and dangers cannot block pigeon’s instinct to return home C．racing horses are able to learn much faster than other horses D．the message paper is carried usually under the wings of the pigeons