Cultures sometimes vary greatly in this regard. A group of researchers in Japan, 16 , studied the facial reactions of students to a horror film.
答案：(D) for example
for example（舉例來說）作插入語，承接前句「不同文化在情緒表達上有很大差異」，接著舉日本研究者的實驗作為具體例子。as usual（一如往常）、in some cases（在某些情況下）、to be frank（坦白說）都不符合這裡「舉出具體研究案例」的語意。
四個選項都是插在主詞與動詞之間的插入語，位置一樣、形態一樣，你會憑語感挑一個。
這是邏輯勾環，而且線索一定要跨句才看得到。前一句是 Cultures sometimes vary greatly in this regard（各種文化在這方面的差異有時很大），是一句通則；本句 A group of researchers in Japan, ______, studied the facial reactions of students to a horror film 講的是日本一組研究者做的一項研究，這是那句通則底下的一個具體個案。從通則走到具體個案，用 for example。填進去讀成 A group of researchers in Japan, for example, studied...（舉例來說，日本一組研究者研究了……）。順帶留意這個位置：轉承語夾在主詞與動詞之間、前後各一個逗號，是常見的擺法，不是只能放句首。
as usual（一如往常）要求前面有一個慣例，這一句是新提出來的研究，不是慣例；in some cases（在某些情況下）雖然也能插在這個位置，但它後面該接的是「某些情況下會怎樣」的通則，而不是一項具體的研究；to be frank（老實說）是說話者要坦白講一件不好說的事，這裡沒有那個語氣。
for example（舉例來說）、as usual（一如往常）、in some cases（在某些情況下）、to be frank（老實說）、vary greatly（差異很大）、facial reactions（臉部反應）。
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.