In certain situations such as in crowded subway cars or elevators, it is not always possible for people to keep their 13 distance from others.
答案：(C) preferred
空格夾在所有格 their 與名詞 distance 之間，須填形容詞，preferred 是過去分詞轉品當形容詞「偏好的」：在擁擠的車廂或電梯裡，人們不見得能與他人保持自己偏好的距離；prefer、preferring、being preferred 都不合。
prefer 這個動詞你很熟（prefer A to B），但很少把 preferred 當成一個形容詞記住：「偏好的、首選的」。看到四個選項都由同一個字變化而來，容易覺得要靠語意分，其實這一題靠位置就能定案。
先看空格卡在哪裡。their ___ distance——前面是所有格 their，後面是名詞 distance，這個位置只能放形容詞。四個選項都是 prefer 變出來的，所以這一格考的是哪一種形式能當形容詞。先把它還原成關係子句看看：the distance which is preferred by them，他們所偏好的距離。既然過去分詞自己就能當形容詞，這一串就可以直接說成 their preferred distance，跟 our preferred way of living 是一樣的道理。其餘三個用同一個方法還原就過不了關：preferring 還原成 the distance which is preferring，語意不通；being preferred 還原成 the distance being preferred，可見 being preferred 只能放在 distance 後面，放不到 their 跟 distance 中間；prefer 是原形動詞，動詞不能當形容詞。這種「過去分詞當形容詞」你國中就用過：a broken window（破掉的窗戶）、fried rice（炒飯）。
preferring 是現在分詞，還原成 the distance which is preferring，語意不通。being preferred 還原成 the distance being preferred，可見 being preferred 只能放在 distance 後面，放不到 their 跟 distance 中間。prefer 是原形動詞，動詞不能當形容詞。
preferred distance／method（偏好的距離／首選方法）、prefer A to B（喜歡 A 勝過 B）、prefer to V（寧可）、required documents（必備文件）、reserved seats（預留座位）、personal space（個人空間）。
Have you been irritated by someone standing too close in line, talking too loud or making eye contact for too long? Or, they may have 11 you with the loud music from their earphones, or by taking up more than one seat on a crowded subway car. You feel unhappy because your personal space has been violated.
According to scientists, personal space involves certain invisible forces imposed on you through all the 12. For example, people may feel their space is being invaded when they experience an unwelcome sound, smell, or stare.
In certain situations such as in crowded subway cars or elevators, it is not always possible for people to keep their 13 distance from others. They learn coping strategies to deal with their discomfort. For instance, people often avoid eye contact with someone standing 14 them, or they pretend that these people are lifeless objects in their personal space. Given the opportunity, they may 15 to a corner, putting distance between themselves and strangers. Or, they may sit or stand equidistant from one another like birds on a wire.