如图16,在△ABC中E是BC上的一点,CE=2BE,点D是AC的中点,设△ABC,△ADF,△BEF的面积分别为S△ABC,S△ADF,S△BEF,且S△ABC=12,则S△ADF-S△BEF= . 答案: .(2010·宁夏银川一中高三上学期第二次月考)31. Alan is a careful driver , but he drives ____ of my friends. A. more carefully B. the most carefully C. less carefully D. the least carefully.