(1) Animals can be divided into vertebrates and invertebrates according to whether there are thorns in their bodies. Vertebrates have thorns in their bodies, while invertebrates have no thorns. Fish, turtles, white geese and frogs all have spines, which belong to vertebrates, while crabs belong to invertebrates without spines.

(2) Crabs belong to arthropods, which are characterized by a tough exoskeleton on the body surface; The body and appendages are segmented.

(3) The forelimbs of the Great White Goose become wings; There are airbags in the body to assist the lungs to complete double breathing, which can supply enough oxygen; Some bones are hollow, some bones heal, and the rectum is very short, so you can lose weight; Developed chest muscles are good for flying.

(4) Frog larvae live in water and breathe through gills. Adults can live on land and in water, breathe with lungs and skin, and belong to amphibians. The tortoise is divided into five parts: head, neck, trunk, limbs and tail. Its body is covered with armor, and it breathes with its lungs. It belongs to reptiles. Therefore, it was chosen as B.

(5) Frog development goes through four stages: fertilized egg, tadpole, young frog and adult frog, which is metamorphosis.

So the answer is: (1) fish, tortoise, big white goose, frog.

(2) Exoskeleton

(3) There is an air bag in the body to assist the lungs to complete double breathing, which can supply sufficient oxygen;

(4)B

(5) abnormal?