单选题 Animals are divided into many groups. Some groups of animals include the, insects, fish, amphibians, reptiles, birds and mammals.
Insects are small animals that have six (21) legs and three body parts (the (22) , the thorax, and the abdomen). Many insects can fly; flying insects have one or two (23) of wings. Some flying insects include butterflies, moths, dragonflies, flies, and mosquitoes. Some (24) insects include springtails, fleas, and lice.
Fish are swimming animals that have scales and fins. Fish (25) oxygen that is dissolved in the water using gills. Most fish have bony skeletons, but some, (26) sharks and rays, have only cartilage.
Amphibians are animals that (27) their life in the water, breathing with gills. As they grow, they breathe air using lungs, and many (28) the land. Some amphibians include frogs, toads, salamanders, and newts.
Reptiles are cold-blooded animals (29) scales, Some reptiles are: the dinosaurs, lizards, crocodilians, and snakes.
Birds are animals (30) have feathers, wings, a beak, hollow bones, and an efficient, one-way breathing system. Most birds can fly, but some (31) . The biggest bird (and the fastest-running bird) is the ostrich, a (32) bird. The smallest bird is a type of hummingbird that is only as (33) as a moth.
Mammals are warm-blooded (34) that nourish their young (using mammary glands) and have hair. Most mammals give birth to live young, but a few primitive mammals (like the duck-billed platypus) lay (35) . Some examples of mammals are whales, bats, cats, dogs, horses, and people.