Air pollution causes airplane accidents because ______.

A．civilization may be doomed if pollution is not controlled
B．pollution is more serious in Europe than it is in America
C．most people do not know that pollution is a serious problem
D．black snow is not so serious compared with white snow

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