功能结构英文

功能词又叫结构词或虚词，指没有完整词汇意义，但是有语法意义或语法功能的词，常见的有代词、数词、冠词、助动词和情态动词，少数副词、介词、连词和感叹词，其数量比较的少，如举例forexample,suchas ，对比while,and,instead,meanwhile，转折but,while,however，因果so,for,because,since,dueto,becauseof，总结inaword,inaconclusion,allinall，列举first,next,what'smore,besides,inaddition……这些都是功能词，希望帮到你……

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart. Their principal function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere. This exchange of gases is accomplished in the mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs called alveoli.To completely explain the anatomy of the lungs, it is necessary to discuss the passage of air through the mouth to the alveoli. Once air progresses through the mouth or nose, it travels through the oropharynx, nasopharynx, the larynx, the trachea, and a progressively subdividing system of bronchi and bronchioles until it finally reaches the alveoli where the gas exchange of carbon dioxide and oxygen takes place.The drawing and expulsion of air (ventilation) is driven by muscular action; in early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, whereas in reptiles, birds and mammals a more complicated musculoskeletal system is used.