Explanation: All animals are multi-cellular. This means that they are made up of many cells/cellular systems. Single-celled organisms, on the other hand, are not considered animals. Those would mostly be too tiny to see without the aid of a microscope tool. The other answer choices would not fit, because not all animals have bones (endoskeletons or exoskeletons). Also, only some animals are cold blooded, which is what the last answer choice has to do with.
