水的总硬度
参考答案：水中钙、镁离子的总量称为水的总硬度。
Everyone is supposed ______ a seat belt in the car. [ ]
A. wearing
B. to wear
C. to be worn
银行的核心竞争力体现在( )。
A．服务B．产品C．品牌D．价格
