Selena has a garden, and she wants to improve the soil so that her plants can grow better. She reads that compost can help improve the soil by adding nutrients to it. Compost is material made from decomposed food scraps, leaves, and grass clippings. Selena plans to make a compost bin so that she can start putting her food scraps and yard waste in it. She reads about several different ways to make compost bins. What would be the best criterion for a successful compost bin design?