How to get to Niu Tianyang Wetland Park?

The animal "Egret" mentioned in the previous sentence belongs to birds and has the characteristics of birds. Its structural characteristics are always adapted to its life. For example, it has feathers on its body surface and its forelimbs become wings, which is suitable for flying; The fuselage is streamlined, which can reduce the resistance during flight; 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 pectoral muscles are conducive to pulling the wings to complete flight movements, viviparous and breastfeeding are not the characteristics of birds. It can be seen that ① the forelimbs become wings, ② the body temperature is constant, and ③ there are airbags in the body.

So choose: B.