160km/h≥线路允许速度vmax＞120km/h地段，钢轨为60kg/m，总磨耗超过12mm时，钢轨为轻伤。
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A tide is called diurnal when（）.
A. only one high and one low water occur during a lunar day
B. the high tide is higher and the low tide is lower than usual
C. the high tide and low tide are exactly six hours apart
D. two high tides occur during a lunar day
正在报请国务院批准的长沙城市总体规划2010年修订版中新增的两个城市组团是什么？
（） are used to limit the pressure in any particular portion and mainly control the pressure after the valve.
A. Relief valves
B. Check valves
C. Safety valves
D. Reducing valve
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