单选题 The primary purpose of paragraph I is to ______.

A、 summarize past research and introduce a new study
B、 describe a historical period
C、 emphasize the advantages of one theory over another
D、 define a term and illustrate it with an example

【正确答案】 D

【答案解析】第一段的主要内容就是提出观点，给出定义，然后举例加以证明。