若 $\frac{x}{3}=\frac{y}{4}=\frac{z}{5}$ ，则 $\frac{x-y-z}{x+3y-z}$ 的值为____．

认识燃烧原理可以合理利用和控制燃烧反应。下列说法正确的是

改革是社会进步的永恒主题。商鞅变法使秦国成了战国后期最富强的诸侯国。请你指出商鞅变法的内容中，对后世影响最为深远的是（　　）

       Basketball is still a young game. It's over a hundred years old. In the winter of 1891, a certain college was having some trouble with its boy students. The weather was bad and the students had to stay indoors. As they couldn't play outdoors, they were unhappy, and some even got into fights from time to time.
       Some of the teachers at the college asked Dr. Naismith to invent（发明）a game so that the students might have something to play with. It was not easy to invent such a game because it had to be played indoors , and the court（球场）was not very large.
Dr. Naismith thought for a few days and invented a kind of ball game. It was a fast, wonderful game with much moving and passing of the ball. It was played between two teams. To make a score , the ball had to be thrown into the basket ten feet（英尺）above
the floor on the wall. At each end of the court there was such a basket. At first, Dr.
Naismith wanted to throw the ball into a box. As he could not find boxes of the right size, he had to use fruit baskets instead. That is how the game got its name.

一个物体的运动方程为其中的单位是米，的单位是秒，那么物体在1秒末的瞬时速度是（   ）