A veterinarian's office runs a "pet hotel", to take care of pets while their owners are away. The office uses a database to keep track of which pet is in which enclosure at any one time. Each animal lives in an enclosure while it is at the hotel. Pets from the same owner may stay together in the same enclosure, if they will be happier that way. An enclosure may be empty, if the hotel isn't full. What statement best describes the participation of the "lives-in" relationship?

• A. A pet has mandatory participation in "lives-in". An enclosure has partial (optional) participation in "lives-in".
• B. A pet has mandatory participation in "lives-in". An enclosure has mandatory participation in "lives-in".
• C. A pet has partial (optional) participation in "lives-in". An enclosure has mandatory participation in "lives-in".
• D. A pet has partial (optional) participation in "lives-in". An enclosure has partial (optional) participation in "lives-in".