单项选择题
A.年年下降B.年年增长C.年年保持不变D.无法做结论
A.A B.B C.C D.D
A.(290+295+293+301)/4 B.(290+295+293)/3 C.(290/2+295+293+301/2)/(4-1) D.(290/2+295+293+301/2)/4