— What _____ your brother want?
— A book. [ ]
A. is
B. are
C. does
D. do
答案：C
等差数列前m项和是30，前2m项和是100，则它的前3m项和是______．
A．拉细绳的力F等于钩码重力G的
B．拉细绳的力F等于钩码重力G的
C．拉细绳的力F等于钩码重力G的
D．拉细绳下降的距离是钩码上升高度的
