正常情况下左反推由哪个液压系统供压()
A.A液压系统
B.B液压系统
C.备用液压系统
D.地面液压源
参考答案:A
个位数字为a,十位数字为b,则这个两位数可用代数式表示为[ ]
A.ab
B.ba
C.10a+b
D.10b+a
It was at ten o'clock _____ he came back. [ ]
A. when
B. after
C. that
D. before