There are two kinds of heroes: heroes who shine in the face of great danger, who perform an 21 act in a difficult situation, and heroes who live an ordinary life like us, who do their work 22 by many of us, but who 23 a difference in the lives of others.
答案：(D) unnoticed
過去分詞 unnoticed 作補語，表示「默默無聞地做他們的工作」（work done unnoticed＝工作完成卻不被注意）；noticing（現在分詞，主動語意方向不合）、noticeable（形容詞「顯著的」，語意相反）、noticed（過去分詞被動，但語意相反，應該是「不被注意」而非「被注意」）都不合。
看到空格後面接著 by many of us，你直覺會想「這是被動，所以填 noticed」，於是選成「被我們許多人注意到」。問題出在你只讀了空格後面那幾個字，沒把整句話讀完。
答對率 43%，鑑別度 60，這題分開的是「有沒有讀到 but」。整句是 heroes who live an ordinary life like us, who do their work ___ by many of us, but who make a difference in the lives of others。but 是轉折，前後必須一正一負。後半句 make a difference（帶來改變）明顯是正面的，那空格所在的前半句就必須是負面的——他們做事不被我們多數人注意，卻真的改變了別人的生命。整句的意思就靠這個 but 鎖死。再看 unnoticed 這個字本身：「朗文當代英語辭典」把它同時列為形容詞與副詞，最常見的搭配是 go unnoticed 與 pass unnoticed（不被注意、被忽略）。這裡的 do their work unnoticed 就是在描述 their work 所處的狀態，還原成 and their work is not noticed by many of us 就通了。
noticing 是主動的「注意到……的」，意義主詞會變成 heroes，「英雄注意著我們許多人」語意不通，而且後面接 by 也接不上。noticeable 是形容詞「顯眼的、明顯的」，方向與 but 的要求相反。noticed 方向同樣相反，它是「被注意到」，跟後面的 but 語意矛盾。三個誘答選項全部倒在同一個地方：沒看 but。
go unnoticed（不被注意、被忽略）、pass unnoticed（悄悄過去而未被察覺）、escape one's notice（逃過某人的注意）、take notice of（注意到）、noticeable（顯眼的、明顯的）、notice sb doing sth（注意到某人正在做某事）。
There are two kinds of heroes: heroes who shine in the face of great danger, who perform an 21 act in a difficult situation, and heroes who live an ordinary life like us, who do their work 22 by many of us, but who 23 a difference in the lives of others.
Heroes are selfless people who perform extraordinary acts. The mark of heroes is not necessarily the result of their action, but 24 they are willing to do for others and for their chosen cause. 25 they fail, their determination lives on for others to follow. The glory lies not in the achievement but in the sacrifice.