水泥熟料矿物中水化速度最快的熟料是（）
A.硅酸三钙
B.硅酸二钙
C.铝酸三钙
D.铁铝酸四钙
参考答案：C
解析：水化速度最快的是铝酸三钙。
Linda has two Chinese friends. _______ often talk in Chinese. [ ]
A. Their
B. Them
C. They
用水灭火时必须具备的条件是瓦斯浓度不得超过（）%。
