Explanation:
A mop and a broom are both cleaning tools that serve a similar purpose, which is to clean floors. Similarly, a museum and a library are both places that serve as sources of knowledge and information, but they serve different purposes.

Relationship between a mop and a broom:
A mop and a broom are both cleaning tools.

Relationship between a museum and a library:
A museum and a library are both places that serve as sources of knowledge and information.

Comparison:
A mop is used for cleaning floors, while a broom is used for sweeping floors. Both tools serve the purpose of cleaning, but they have different methods of achieving it. Similarly, a museum and a library both serve as sources of knowledge and information, but they have different ways of presenting and preserving that information.

Difference between a museum and a library:
A museum is a place where collections of objects or artworks are displayed for educational or artistic purposes. It typically showcases exhibits that are related to history, art, science, or culture. Visitors can view these exhibits and learn about the subjects they represent.

On the other hand, a library is a place where books, magazines, journals, and other written materials are stored and made available for borrowing or reading. Libraries offer a wide range of subjects and topics, allowing people to access information on various subjects.

Conclusion:
The relationship between a mop and a broom is that they are both cleaning tools. Similarly, the relationship between a museum and a library is that they are both sources of knowledge and information, but they serve different purposes. Therefore, the word that best completes the relationship is "library" (option A).