Railcars on tickets missing

Several rail passengers were recently told that the cars shown on the tickets they had purchased on the Internet did not exist. A traveler said the staff even claimed that they had bought the tickets from scalpers, commonly known as huangniu in China. Officials admitted that although rare, sometimes it does happen when the cars are temporarily taken out of service due to maintenance or some other reason.

Why are the railcars missing?

A. because the tickets were bought online

B. because the tickets were bought from the scalpers

C. because the cars are temporarily taken out of service

（中国日报网英语点津 Helen 编辑）