Question 18 is based on the recording you have just heard.

18. What question does the speaker think is interesting about Sternberg’s three elements of love?

解析：D。本题目为细节题。问题为：基于Robert Sternberg的爱情三元理论，讲话人认为什么是有趣的？原文所在句： Now what’s interesting about the theory is what do you have if you only have one out of three or two out of three.这个理论比较有趣的一点是，假如你只有三个因素中的一个因素或者两个因素，那么会怎么样？选项D) How the relationship is to be defined if anyone is missing（如果任何一个元素缺失，这段关系会被定义成什么？）与原文含义最为一致。