7.High School English Listening

Most of us know balloons from festivals and fun fairs, where they are colorful and amusing, but in the 19th century, before airplanes were invented, balloons were used in wartimes to spy on the enemy position.
One or two men would go up with a telescope in a balloon tied to the ground with a rope.
However, because the enemy might fire a cannon at them, this was dangerous.
So before men would go up in a balloon, they would first float (or send up) a trial balloon without any men in it to test the situation.
If the enemy tried to shoot that trial balloon, the men would not go up.
From this origin, today we use this idiom in any situation where we want to measure public reaction or opinion before committing a lot of money and effort to some project.
译文：
我们大多数人都是在节日和游乐场所认识气球的，它们色彩斑斓，令人捧腹，但在19世纪，在飞机被发明之前，气球在战争时期被用来监视敌人的位置。
一个或两个人将带着望远镜上天，在气球里用绳子绑在地上。
然而，由于敌人可能向他们发射大炮，这很危险。
因此，在人们乘坐气球上天之前，他们会先漂浮（或送上）一个没有任何人员的试验气球来测试情况。
如果敌人试图射杀这个试验气球，人们就不会上去了。
从这个渊源来看，今天我们在任何情况下都会使用这个成语，即在对某个项目投入大量资金和精力之前，我们要衡量公众的反应或意见。
重点词汇：
spy on 监视 ; 窥视 ; 侦查
enemy position 敌军位置
send up 使升高 ; 取笑，嘲弄 ; 判…入狱 ; 对…判刑
trial balloon 试探性言论
want to 应该