给出下列四个命题：（1）如果某圆锥的侧面展开图是半圆，则底面半径和母线之比为1：2；（2）若点A在直线y=2x-3上，且点A到两坐标轴的距离相等，则点A在第一或第四象限；（3）半径为5的圆中，弦AB=8，则圆周上到直线AB的距离为2的点共有四个；（4）若A（a,m）、B（a -1,n）(a0)在反比例函数$y=\frac{4}{x}$的图象上，则mn。其中，正确命题的个数是（   ）

(二)

    This is my room. Near the window there is a desk. I often do my homework at the desk. You can see some books, some flowers, a ruler and a pen on it. On the wall near the desk there is a picture of a cat. There is a clock above my bed. I usually put my football under my bed. There is a chair in front of the desk. I can see the trees and the roads outside when I sit there.

 阅读短文，选择最佳答案。

边长为5,7,8的三角形的最大角与最小角的和是（  ）