水泥是水泥混凝土的主要原料之一，它是一种（）胶凝材料
A.水硬性
B.气硬性
参考答案：A
His sister's never been to the Summer Palace, _____? [ ]
A. is she
B. has she
C. hasn't she
D. isn't he
NAVTEX发射类型为（）
A.J3E
B.AIA
C.G3E
D.FIB
