单项选择题The company had about 20 notebook computers but only one-third _______ used regularly. Now we have 60 working all day long. A.is B.are C.was D.were
单项选择题用偏压法计算横隔梁内力的力学模型是将中衡隔梁近似地视作竖向支承在多跟弹性主梁上的多跨弹性支承简支梁。()