The air sac system is bigger than the lungs and takes up 15 percent of the chest and belly area.

　　Meanwhile，the bird’s great oxygen needs are also handled by the internal breathing system. The oxygen，stored primarily in body fat tissue，is burned through the process of cell respiration. This process produces both muscular energy and heat.

　　How does a bird breathe？

　　Ways to get oxygen For birds and dogs，by breathing in air For fish，from 1. ________through its body

　　Two 2. ______systems Internal and external

　　External respiration system Using the lungs and a series of air sacs To communicate with body parts 3. ________

　　4. ____sac system Bigger than the lungs

　　Taking up a 5. ______part of the chest and belly area

　　6. ______of bird breathing A stream of air

　　▲going through lungs without 7. ______

　　▲being channeled through the complex system of air sacs and through 8. ________bones

　　▲being

　　9. ______forward through the lungs again，then through more air sacs

　　▲ 10. ______in the windpipe and are expelled from the body

　　答案：1. water　2. respiration　3. directly/straight　4. Air　5. small　6. Process 7. stopping/stop 8. hollow 9. channeled　10. completing/finishing/ stopping

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