用起重机吊起一个40吨重的物体,吊索最多可承受50吨的拉力,吊索本身的重量可不计,物体吊在空中静止时,吊索所承受的拉力是多少?()
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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