根据《危规》规定，危险货物按其主要危险性和运输要求分为（）类。
A.十类
B.九类
C.八类
D.七类
参考答案：B
With the country's population reaching 1.6 billion in the mid of this century, most of China's rivers,
including the Yellow River, ____.[ ]
A. is drying up
B. will be drying up
C. dry up
D. have dried up
untry's population reaching 1.6 billion in the mid of this century, most of China's rivers,