Air pollution causes airplane accidents because ______.

A．without computers, there would be no modern science
B．computers are more intelligent than human beings
C．computers will replace everything in the future
D．computers never make mistakes

A．so people like it better than before
B．but there is still a big gap between different classes
C．all the people there lead a very happy, life
D．all the industries and companies are in the hands of the goverment