Concept:A good mathematics textbook is one that supports learning through clear explanations, solved examples, and ample practice material.
Explanation:The subject matter in a good textbook should be arranged from simple to complex and from concrete to abstract.
It should use simple, clear, and child-friendly language.
A good textbook must contain many solved examples to help students understand concepts clearly.
It must also provide a large number of practice questions to reinforce learning and develop problem-solving speed.
Practice questions also help students apply the error-correction method and gain confidence.
Therefore, the defining feature of a good mathematics textbook is that it contains a lot of questions for practice.
Answer:C. questions for practice