If that's how we're defining digital textbooks, there's no hope of that becoming a mainstream product.
出自-2013年6月阅读原文
英语六级真题
As Yale law professor Anne Alstott argues, justifying parental support depends on defining the family as a social good that, in some sense, society must pay for.
出自-2010年6月阅读原文
Economic inequality is the "defining challenge of our time".
2015年12月六级真题（第三套）阅读 Section C
柯林斯高阶英汉双解学习词典释义
VERB
阐明;规定;限定;使明确
If you define something, you show, describe, or state clearly what it is and what its limits are, or what it is like.