父子年龄之和是60岁，且父亲年龄是儿子年龄的4倍，那么儿子的年龄为 [ ]
A.15岁
B.12岁
C.10岁
D.14岁
B.
Luckily，we’d brought a road map without____we would have lost our way.
A．it
B．that
C．this
D．which
脱磷站分配器下方采用流态化床直径为（）。
A.￠300mm
B.￠800mm
C.￠600mm
D.￠400mm
