Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to know if a pet guinea pig is ill [title] Check its eating patterns. [step] It is not far from the truth to say that healthy guinea pigs eat constantly, so any changes in eating patterns or frequency should always be cause for concern. Sometimes, not eating or eating less than usual may be the only observable sign of a serious condition.

Ending1: If your guinea pig is lethargic, has appetite issues or displays odd behavior, report these to your vet. This is especially important if your pet's eating habits are seasonal or if you bring your pet home when it needs to be cleaned or put to sleep. Ending2: [substeps] Guinea pigs cannot go more than a few hours without eating before causing potential damage. If your pet has not eaten at all (or very little) in the past 16-20 hours, seek immediate veterinary attention. Ending3: [substeps] It may also be signs of a large health concern such as pelvic inflammatory disease. [title] Monitor your pet's urination. Ending4: [substeps] If a guinea pig eats more frequently than you would expect, it may be ill. A sick guinea pig may refuse food for fleas, ticks, or parasites if it has a condition like psoriasis.

Answer format: ending1/ending2/ending3/ending4