Explanation:

Introduction:
In the given options, the correct answer is option B, which states "Little fat books." Let's understand why this option is the correct answer.

Understanding the Options:
To find out who stood by themselves, we need to analyze the options given in the question.

- Option A: Tall skinny books
- Option B: Little fat books
- Option C: Door
- Option D: Chairs

Analysis of the Options:
- Option A: Tall skinny books
Tall skinny books are usually placed together on a bookshelf and are not likely to stand by themselves. Therefore, option A is not the correct answer.

- Option B: Little fat books
Little fat books are small in size, and their width is relatively larger than their height. As they are small and have a wider base, they have a higher chance of standing by themselves. Therefore, option B is the correct answer.

- Option C: Door
A door is a large object that requires support from hinges or a frame to stand upright. Therefore, option C is not the correct answer.

- Option D: Chairs
Chairs are designed to be used by people for sitting and require the weight of a person to balance and stand. Therefore, option D is not the correct answer.

Conclusion:
Among the given options, "Little fat books" are the most likely to stand by themselves due to their small size and wider base. Therefore, the correct answer is option B.