正常成年人体液总量约占体重的（）。
A.40%
B.50%
C.60%
D.70%
E.80%
参考答案：C
In one corner of the garden there stands a little board，_______“Keep off the grass．”
A．On which writes
B．it says
C．on which is read
D．which reads
原子序数为12的镁（Mg），核外电子分布于（）个电子层上.
A.3
B.4
C.2
D.1
