Book metaphor:

1. Books are the ladder of human progress.

2. Books are nutritional books in the world and the ladder of human progress.

3. Books are the president of human knowledge.

4. Books are tools for cultivating the soul.

5. Books are tools for cultivating wisdom.

6. Books are the ladder of human progress.

7. Books are the key to wisdom.

8. Books are ladders that help people reach the peak of their ideals.