用如图所示的四种机械提起同一重物,不计机械自重和摩擦,最省力的是 [ ]
A.
B.
C.
D.
答案:D
Mr Brown has asked Tom, Cathy, Louis and _____ to go to the school library.[ ]
A. myself
B. mine
C. I
D. me
下面的数组声明中,正确的是( )。
A. k=7 b=14
B. k=6 b=6
C.k=4 b=8
D.k=1 b=7