仔细阅读理解 — 英语阅读题

Read the following passage and answer the question. When Marcus transferred to a new university, he expected his part-time job at the campus library to be an easy way to earn money. Instead, it changed how he studied. Watching which books students actually borrowed, he noticed that the most popular titles were not the textbooks on his own reading list but older books recommended by professors during lectures. He began borrowing those books himself, and within a term his essays were receiving higher marks, though he spent no more hours studying than before. His roommate Chen, by contrast, bought every textbook on the syllabus but rarely opened the ones not required for assignments. At the end of the year, the head librarian asked Marcus to train new student assistants, saying that his habit of observing rather than merely following instructions was exactly what the library valued. Question: What can be inferred from the passage? A. Marcus earned more money at the library than Chen did. B. Marcus improved academically by following his professors' informal recommendations rather than only the required reading list. C. Chen failed all his courses because he bought too many textbooks. D. The head librarian required all student assistants to read older books.