塑料瓶底的数字，是什么意思？

Many plastic bottles have a small triangle. 很多塑料瓶底都有一个小三角。 A number from 1 to 7 sits inside. 三角中间写着1到7的数字。 Each number means a different plastic. 每个数字代表一种不同的塑料。 Number one is PET, used for water bottles. 1号是PET，用来做矿泉水瓶。 Recycling plants sort plastics by these numbers. 回收站靠这些数字给塑料分类。 So the number tells workers how to reuse it. 数字告诉工人，这个瓶子该怎么回收。