4. 有一如圖之懸臂樑,w為分佈負載,當以微分方程式Ely(v) = -w 求解其撓曲函數y(x)時,下列之邊界條件何者錯誤?(A)at x = 0, y = 0 (B) at x = 0, y' = 0 (C) at x = xp, y' = 0 (D) at x = XB, y" =0。