硬度合金是用硬度和熔点很高的碳化物粉末和金属黏结剂，高压压制成型后，再高温烧结而成的粉末冶金制品．
参考答案：对
Why have the Americans developed space shuttle according to the passage
A．It is a first step to explore outer space.
B．It is a follow-up action of the Apollo moon landings.
C．It is a compromise to the exorbitant human expeditions to the Mars.
D．It is a compensation for the wishful thinking of human landing on the Mars.
ZPW2000轨道电路在轨道电路任一处轨面用标准分路线进行分路时（电气绝缘节区域死区段除外，进行电压和电流测试。接收器的限入残压不应大于（），轨道继电器残压不应大于5V，并可靠落下。
A、100mV
B、120mV
C、140mV
D、160mV
