"I didn't like the ending," I said to my favorite college professor. It was my junior year of undergraduate, and I was doing an independent study on Victorian literature. I had just finished reading The Mill on the Floss by George Eliot, and I was heartbroken with the ending. Prof. Gracie, with all his patience, asked me to think about it beyond whether I liked it or not. He suggested I think about the difference between endings that I wanted for the characters and endings that were right for the characters, endings that satisfied the story even if they didn't have a traditionally positive outcome. Of course, I would have preferred a different ending for Tom and Maggie Tulliver, but the ending they got did make the most sense for them.

上面一段摘自2024高考英语全国甲卷阅读理解D。这里的undergraduate是不可数名词吗？不对啊，词典上查到的它是可数名词。变成复数吗？好像也不对。请教专家如何解释，谢谢！