下列最能说明鲸鱼是哺乳动物的是（    ）

    Mr. Brown works on a farm. Mr. Green works in a park. But they don't know each other. Today is Sunday. Mr. Brown comes to the park. He feels tired. He wants to have a little rest. He sees a red chair under a tree over there. So he walks to the chair. Mr. Green is behind him. Mr. Green runs to the chair with a board when he sees Mr. Brown come to the chair. But Mr. Brown runs faster（更快） than Mr. Green. Then he sits on the chair. Mr. Brown is very happy. But Mr. Green doesn't say anything. He gives the board（板子） in his hand to Mr. Brown. It says, "Wet Paint(油漆未干). "

某厂第二车间每小时生产零件243个，要生产零件3159个，需要____小时．

使得关于x的不等式组 $\sqrt{A{B}^2-A{D}^2}=\sqrt{{10}^2-8^2}=6$ 有解，且使分式方程 $\frac{DE}{DB}=\frac{DB}{AD}$ 有非负整数解的所有的m的和是____