下列不属于货物透气系统的是:()
A、惰性气体管线
B、风机
C、挡火帘
D、透气x管
参考答案:B
Tom ________ in the library every night over the last three months.[ ]
A.works
B.worked
C.has been working
D.had been working
若∠A=30°,则∠A的余角等于( )度。