translation.en: By using open educational resources and the generosity of professors who are putting their material free and accessible, we don't need to send our students to buy textbooks.
translation.zh: 使用开放的教学资源 以及教授们的慷慨馈赠， 很多教授把他们的教学材料 免费公开， 我们不需要让我们的学生去购买课本