Observe the red-green light changes in the column and learn the environmental protection knowledge level of one's self.

观察立柱内红绿灯光的变化，了解自己的环保情况。

youdao

Observe the red-green light changes in the column and learn the environmental protection knowledge level of one's self.

观察立柱内红绿灯光的变化，了解自己的环保情况。

youdao