B.错误,例如:n = 2k时,取u[n] = 1/(2n),n = 2k-1时,取u[n] = 0.这样∑{1 ≤ n} (-1)^n·u[n] = ∑{1 ≤ k} u[2k] = ∑{1 ≤ k} 1/(4k),发散.D.正确,由0 ≤ u[n] < 1/n,有0 ≤ u[n]² < 1/n².根据比较判别法...