题目:设函数f(x)在(a,b)内可导,且f′(x)<0,则对于任意x1?,x2?∈(a,b),且x1?<x2?,有( )。A. f(x1?)>f(x2?)B. f(x1?)<f(x2?)C. f(x1?)=f(x2?)D. 无法确定f(x1?)与f(x2?)的大小关系