This is the Japanese norm for feelings of distress 20 someone in authority, which explains why the students masked their upset with a poker face in the experiment.
答案：(B) in the presence of
【句型】in the presence of + 人，固定搭配，表示「在……面前／在場」，符合「在權威人士（老師）面前隱藏負面情緒」的日本文化規範語境，呼應段落開頭「老師在場」的實驗設定。with the help of（在……的幫助下）、on top of（在……之上）、in place of（取代）都不符合這裡的語意。
四個選項都是「介系詞加名詞加 of」的多字介系詞，長得很像，你會憑哪個最眼熟就直接選它。
這是主題勾環：這一句在替全篇的實驗場景下結論，要找的是能扣回那個場景的說法。整句是 This is the Japanese norm for feelings of distress ______ someone in authority（這是日本人面對______有權威的人時，處理不安情緒的常態）。空格後面接的是「人」，而全篇的實驗場景就是「老師在場的時候學子面無表情」，所以空格要的是「在某人面前、當著某人的面」，也就是 in the presence of。presence 是形容詞 present（在場的）的名詞形，同一篇第 17 題的 with the teacher present 講的正是同一件事，兩題一個用形容詞、一個用名詞，把「在場」這個概念的兩種寫法都考過了。填進去讀成 feelings of distress in the presence of someone in authority。
with the help of（在……的幫助下）方向不對，權威者在場不是在幫忙，反而是壓力來源；on top of（在……之上；除……之外）講的是位置或追加；in place of（代替、取代）要有一個被取代的東西，這裡沒有。三個都是多字介系詞，形態吻合，容易被順手選走。
in the presence of（在……面前、當著……的面）、presence（名詞：在場、出席）、someone in authority（有權威的人）、with the help of（在……的幫助下）、in place of（代替、取代）、a poker face（面無表情的臉）。
People may express their feelings differently on different occasions. Cultures sometimes vary greatly in this regard.
A group of researchers in Japan, 16, studied the facial reactions of students to a horror film. When the Japanese students watched the film 17 the teacher present, their faces showed only the slightest hints of reaction. But when they thought they were alone (though they 18 by a secret camera), their faces twisted into vivid mixes of anguished distress, fear, and disgust.
The study also shows that there are several unspoken rules about how feelings should be 19 shown on different occasions. One of the most common rules is minimizing the show of emotion. This is the Japanese norm for feelings of distress 20 someone in authority, which explains why the students masked their upset with a poker face in the experiment.