一氧化碳具有（），高温时能从金属氧化物中夺取氧而使金属还原。
A.氧化性
B.还原性
C.毒性
D.难溶水性
参考答案：B
—I ______ for you for two hours, but in vain. Where did you go?
—I ______ at my uncle’s.
A．had looked; may have stayed
B．looked; must have stayed
C．have looked; may be staying
D．looked; must be staying
堆取料机照明电压等级是（）V。
