Women and youth in rural Southern communities now constitute the fastest growing segment of people with AIDS. (Para.2)
Meaning: The number of women and young people who are infected with AIDS is growing fastest in the countryside in the South.
constitute: vt. make up; form
Seven days constitute a week.一周有7天。
Twelve scientists constituted a research group to study air pollution.12位科学家组成一个研究小组研究空气污染。
Real familiarity with a 3,000 word vocabulary constitutes a good base for further English language learning. 真正掌握了3000单词，就具备了进一步学习英语的基础。
segment: n. any of the parts into which something may be divided
The company controls this segment of the market. 这个公司控制了这部分市场。