The body of an animal may compare to some machine such as a locomotive. In fact, the body of an animal itself is a machine, which is composed of many parts. Each part plays a special role, with special structure supporting it. All of the parts rely on and cooperate with each other, in order to fulfill the operation(fulfill和operation搭配有點怪) of the machine. A locomotive has to be added (with) fuel, such as coal, firewood, or other flammable substance, consuming which(分詞跟這樣的clause好像不常見，見到過分詞+what從句，不太確定你這個對不對，可以改為consumption of which或者另起一句) may provide motion or energy for the machine. The body of an animal also need（s） fuel supplementation being called food, which may provide（provides） energy to the animal. In order to ignite the flammable substance and oxidize the food in the animal body, oxygen is essential. （病句，還是我上次跟你說的人稱問題， 可以說：Oxygen is essential in doing something，也可以說Oxygen is needed to do something. 我覺得如果非要用 In order to…, 主語得是人， in order to ignite the flammable substance, we need to add oxygen. ） The locomotive is composed of special parts: the hearth to accept（accept用的有點怪，accept很少主語是物，因為有主觀性，接受/拒絕) and ignite the flammable substance, the pipe to transport steam, the wheel to make the locomotive move on（怪，這裏用從句可能好點， the wheels that enable the locomotive to move）, and the chimney to exhaust gas. While（while用得不對，我覺得while如果在句首，後麵的句子常常表轉折。可以換成Similarly，the animal body…） the animal body is also composed of different parts: gastrointestinal tract to ingest and absorb food, the emunctory organ to evacuate waste, the arteries and veins to transport oxygen and store nutriment, and the legs and wings to move on(和前麵一樣，用從句好點兒。去掉on好像好一點兒，就像說：The animal body needs the legs and wings to move around. ).
