换热器热油的流动方向一般是()
A.上进上出
B.上进下出
C.下进上出
D.下进下出
参考答案:B
——Hey, you haven’t been acting like yourself. Everything OK?
—— .
A.I’m fine, thanks
B.Sure, it is
C.That’s good
D.It’s OK
满足m2+n2+2m-6n+10=0的是( )
A.m=1,n=3
B.m=1,n=-3
C.m=-1,n=-3
D.m=-1,n=3