A museum collects, protects and shows objects that tell us about the past, nature or art. Some museums, such as national museums, are very large, while others are small and focus on one subject, such as coins or trains. In the past, visitors were usually asked to look but not to touch. Today, many museums try to make visits more active. Children can try on costumes, touch models and use screens to explore ancient places. Many museums also offer free online tours, so people who live far away can enjoy the collections. Behind the scenes, workers study objects carefully, clean them and keep them at the right temperature, since heat, light and damp can destroy old paper or cloth. In this way, museums help future generations to learn from the past.

Question: What is the writer's purpose in the last sentence?