球墨铸铁QT450-10的基体是() ["A.铁素体","B.铁素体+珠光体","C.珠光体","D.珠光体+渗碳体"]
确定装配的检查方法,应根据()结构特点和生产类型来选择。 ["A、零件","B、标准件","C、外购件","D、产品"]
火灾现场尸体的证明作用有()。 ["A、证明火灾性质","B、证明起火部位","C、证明火灾原因","D、证明起火时间"]
选用装配用设备及工艺装备应根据()的结构特点和生产类型选用与之相应的装配设备。 ["A、零件","B、购件","C、产品","D、标准件"]
球墨铸铁中的球化剂为() ["A.Mn","B.Al","C.Mg","D.Si"]
豆科分几个亚科?简述亚科的主要特征。