在钢梁端部、拱桥温度伸缩缝和拱顶等处前后各（）m范围内不得有钢轨接头。
A、2m
B、3m
C、4m
D、5m
参考答案：A
His aunt wanted to have him _______ the radio, but he had had it ________ already.
A．repair, repair
B．to repair, repair
C．repaired, to repair
D．repair, repaired
设NA为阿伏加德罗常数，下列叙述中正确的是：
A．常温下11.2L的甲烷气体含有甲烷分子数为0.5NA个
B．标准状况下，11.2L四氯化碳所含分子数为0.5 NA
C．14g乙烯和丙烯的混合物中总原子数为3NA个
D．1L、0.1mol/LH2SO3溶液中含SO32-离子数为0.1NA个
