单选题 ______ American universities produce great research and great graduate programs, they sometimes pay little attention to the teaching of undergraduate students.
A. When B. While C. As D. Since

【正确答案】 B
【答案解析】while在此引导让步状语从句。题句意为：“虽然美国的大学在科研和研究生培养方面做得很不错，但有时对本科生教学不怎么重视。”