繪本: im.g.1.9.4.Another Layer
Attribution:
illustrative mathematics. geometry. unit 1. section 9. activity 4. "Another Layer"
https://im.kendallhunt.com/HS/teachers/2/1/9/index.html
Licensed under the Creative Commons Attribution 4.0 license
https://creativecommons.org/licenses/by/4.0/
