We might forgive people who let their manners slip, but we'll feel more positive about and strongly connected to those who 20.
答案：(A) don't
those who don't（那些沒有這樣做的人）don't 在此為助動詞構成的代動詞用法，代替前面省略的 don't let their manners slip。全句與前文的 who let their manners slip（禮儀失當的人）形成對比，表示相較於偶爾禮儀失當的人，我們對那些「始終保持禮貌、未曾失禮」的人感覺更正面、也更緊密相連；do／are／aren't 均不符合此處的否定對比語意與動詞型態。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
空格在句尾，後面什麼都沒有，很容易覺得句子還沒寫完而不知道該填什麼；看到 those who 也有人反射性地想找形容詞，於是挑了 are 或 aren't。
這一格考的是替代——用一個助動詞代替前面剛出現過的整串動作，避免重複。國中就學過：Do you like it?—Yes, I do.（do 代替 like it）、When in Rome, do as the Romans do.（後面那個 do 替代前面的動作）。本題被代替的動作就在同一句前半：let their manners slip（讓自己的禮節鬆懈）。整句用 but 分成一正一反——前半是「我們也許會原諒那些禮節鬆懈的人」，後半要講的是相反的一群人，也就是「不讓自己禮節鬆懈的人」，those who don't ＝ those who don't let their manners slip。把被代替的動作還原出來讀一次就確定了。這裡也用得上並列的三步判準：對等連接詞是 but，它連的是兩個子句，依據寫在左邊那一半，右邊照著它反過來說。
do 方向相反，會變成「我們對那些同樣讓禮節鬆懈的人感覺更好」，與 but 要求的轉折矛盾。are 與 aren't 是 be 動詞，代替不了 let their manners slip 這個一般動詞的動作——要被代替的是什麼詞類的動詞，就得用同一類的助動詞；而且 those who are 後面缺補語，句子並不完整。
those who ＋ 動詞（……的那些人）、let one's manners slip（禮節有所鬆懈）、do 代替前面出現過的動作（例如 Yes, I do.）、feel positive about（對……感覺良好）、be connected to（與……有連結）、forgive somebody（原諒某人）
Having good manners is more than just being nice. Good manners make the social world easier to navigate. They provide guidelines to 16 in times of uncertainty and reduce the chance of awkward exchanges. For example, knowing who is supposed to go first or have a seat keeps us from having to negotiate every time. A world 17 good manners would be confusing and potentially confrontational.
Good manners certainly connect people to their 18 environment. Respecting good manners shows a desire to actively engage with a community and the people in it. 19 to adopt good manners sets people apart.
We might forgive people who let their manners slip, but we'll feel more positive about and strongly connected to those who 20. Good manners are very important because they teach us the proper way to behave in society.