慢速英语:High and Fast: the X-15 Reached the Edge of Space

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短语讲解：

1. After three minutes, its fuel has burned up.

burn up 燃烧起来
例句：Usually they burn up about 100km above the earth.
它们常在地球上空约100公里处被烧毁。

2. They were designed to fly at speeds up to six thousand four hundred kilometers an hour.

speed up 加速
例句：We'll have to speed up to make up for lost time.
我们必须加快速度弥补失去的时间。

3. That was more than seven times the speed of sound.

more than 多于
例句：Do not attempt more than four.
不要企图超过四次。

4. It decided to end the X-15 program. Many space experts disagreed with the decision.

decide to do 决定做
例句：Once you decide to do something, you must try to do it well.
一旦你决定做什么事，就要把它做好。