有一台多级泵(八级),流量Q=45m3/h,扬程H=160m,转速n=2900r/ min,则比转数ns=( )
A.150 B.120 C.80 D.60
参考答案:B
— _____________ are you?
— I'm nine. [ ]
A. What
B. How
C. How old
如果(x-1)(x+4)=x2+mx+n,那么m,n的值为( )
A.m=5,n=5
B.m=5,n=4
C.m=3,n=-4
D.m=-3,n=5