采用遮栏或外护物防护，其外壳防护等级不应低于（）。
A.IPX
B.IP2X
C.IP3X
D.IP4X
参考答案：B
His father looks young, but _____ fact he is _____.
A．in; in the forties
B．in; in his forties
C．in the; in the forties
D．in; in his forty
1990年与1979年相比，第三产业占国民生产总值的比重增加（）
A．23.0%
B．25.0%
C．2.0%
D．18.1%
