水处理用石英砂滤料的密度不应小于（）g/cm3（CJ24•1—88）。
A.1.95
B.2.15
C.2，05
D.2.55
参考答案：D
The teacher told the pupils that the United States of America _____ 50 states.
A．was made of
B．made up
C．makes up
D．is made up of
王安石变法的内容和作用。
