In 21 , the brain waves of a sleeping person are similar to those of a waking person, and the eyes move about rapidly under the closed lids. 22 kind of sleep is Non-Rapid Eye Movement sleep.
答案：(A) this
this 指代前面提到的 REM sleep（這種睡眠中），「In this [kind of sleep]」；each（每個，不特指REM）、both（兩者，這裡只講一種）、those（那些，不合單數指代）都不合。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
四個選項都是很短的指示詞或代名詞，中文都能翻成「這個、每個、兩者、那些」，擺進 In ___ 裡唸起來都不算太怪，於是很容易隨手挑一個。這一格要看的是「前一句到底交代了幾樣東西」。
四個選項都是擺在介系詞 In 後面的指示詞，可見這一格考的是它指向前面的什麼，那就回頭讀前兩句。第一句說 there are two kinds of sleep（睡眠有兩種），第二句說 One is Rapid Eye Movement (REM) sleep（其中一種是快速動眼期睡眠）。所以到目前為止，被點名的只有一種，這一句接著要描述的就是它。In this 等於 in this kind of sleep（在這種睡眠中），用一個近指的 this 把剛剛講過的那一種收攏起來再指一次，這叫回指（Halliday 與 Hasan「Cohesion in English」的指稱銜接）。同型的題目在題庫裡反覆出現：94 年第 28 題的 this discomfort 回指前文的 feel pain，92 年第 22 題的 this problem 回指「得在太空衣裡如廁」這件事，判斷的順序都一樣——先問「這個 this 指的是前面哪一段」，再看選項哪一個接得住。
both（兩者）：In both 是「在兩者之中」，但這一句描述的腦波與眼球活動是 REM 睡眠獨有的特徵，下一句才輪到另一種，用 both 等於把兩種混為一談。each（每一個）：要有一組東西可以一個一個分配，而前一句只點名了一種，還沒有一組可分。those（那些）：複數而且是遠指，前面只有一種睡眠，數量和距離都對不上。
in this case（在這種情況下）、be similar to（與……相似）、rapid eye movement（快速動眼）、move about（四處移動）、under the closed lids（在閉著的眼皮底下）、two kinds of（兩種……）。
Basically, there are two kinds of sleep. One is Rapid Eye Movement (REM) sleep. In 21 , the brain waves of a sleeping person are similar to those of a waking person, and the eyes move about rapidly under the closed lids. 22 kind of sleep is Non-Rapid Eye Movement sleep.
Scientists have discovered that dreams happen mainly in REM sleep. Everyone dreams about 20 percent of their sleeping time. 23 people who say they never dream show about 20 percent of REM sleep. 24 these "non-dreamers" do their sleeping in a laboratory 25 researchers can wake them up and ask them whether they were having dreams the moment before, it 26 that they dream as much as others.
Events in daily life sometimes occur symbolically in dreams. 27 , a boy is having difficulties on the school playground because a bigger boy keeps bullying him. He may dream at night of being alone in the playground, 28 a lion. At other times the dreaded event from daily life simply occurs in a dream in its real-life form; 29 , the boy dreams of being bullied by the bigger boy.
30 scientific research, we have known more about the relationship between sleep and dreams. However, why a dream will take a certain symbolic form is still a mystery.