According to regulations，a cargo hose used for transferring liquefied gases must have a bursting pressure of（）.
A. 5 times the maximum working pressure on the hose during cargo transfer
B. one half the designed working pressure
C. 4 times the pressure of the cargo pump used for transferring
D. 5 times the minimum working pressure on the hose during cargo transfer
查看答案
垄断竞争条件下资源配置效率不如完全竞争的原因在于产品差别的存在。
A. 正确
B. 错误
润滑油不仅有减小运动副摩擦、磨损的作用，而且具有冷却、清洁、密封、防锈的作用。
A. 正确
B. 错误
氟化物含人体必需的微量元素，饮用水含量过高或过低都不宜，它的适宜质量浓度为（）
A. 0-1.0mg/L
B. 0.5-1.0mg/L
C. 0.5-2.0mg/L
D. 1.0-2.0mg/L
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