According to conventional theory, yawning takes place when people are bored or sleepy and serves the function of increasing alertness by reversing, through deeper breathing, the drop in blood oxygen levels that are caused by the shallow breathing that accompanies lack of sleep or boredom.(TPO18, 45)

　　conventional /kən'vɛnʃənl/ adj. 傳統(tǒng)的;老套的，千篇一律的;約定的

　　alertness /ə'lə:tnis/ n. 警戒，機敏

　　reverse /rɪ'vɜːs/ v. 使(某物)反轉(zhuǎn); 將(某物)翻轉(zhuǎn);轉(zhuǎn)變

　　我是分界線，大家先一遍速讀看是否理解

　　(According to conventional theory), yawning takes place (when people are bored or sleepy)and serves the function (of increasing alertness) (by reversing, through deeper breathing, the drop in blood oxygen levels) (that are caused by the shallow breathing) (that accompanies lack of sleep or boredom).(TPO18, 45)

　　托福閱讀長難句100句分析：

　　這個句子的主干就是：

　　yawning takes place and serves the function

　　修飾一：(According to conventional theory)，介詞短語

　　中文：根據(jù)傳統(tǒng)理論

　　修飾二：(when people are bored or sleepy)，從句

　　中文：當人們感到厭煩或困倦時

　　修飾三：(of increasing alertness)，介詞短語

　　中文：增強警覺

　　修飾四：(through deeper breathing)，插入語

　　中文：通過深呼吸