According to the passage, the average number of people killed annually in traffic accidents around the world is _________.

A．Automobile and Economy
B．Automobile and the Environment
C．The Problems with the Automobile
D．Advantages and Disadvantages of the Automobile

A．are an important part of the world' s economy
B．are becoming less dangerous
C．will produce less air pollution in the future
D．are killing more people in recent years than in the past