单项选择题

C

Adopt-A-Book at Leeds University Library
Is there a book that means a lot to you A book that has encouraged you A book that is of great value in the history of a subject you care about A book with some personal importance to you A work by Shakespeare, Isaac Newton, Tolkien—or something only you would think of
If there is, there may well be a copy in Leeds University Library’s Special Collections, and from as little as ￡25 you can Adopt-A-Book at Leeds. We will place a bookplate in the book recording your support for the Library. You can also adopt a book as a gift for someone else—perhaps to celebrate a special event, like a birthday or wedding.
Please help us to protect our rare (珍稀的) books and keep them safe for present and future users. Our copies of many of the most important works ever printed are kept in safe conditions and the collections are well known worldwide. They are consulted (参阅) by thousands of students and researchers visiting from all over the world, and you may have worked with the valuable works yourself during your studies. When you adopt a healthy book, you help us to revive (使复苏) another that’s not so fit!

What does the underlined word "they" (Line 3, Para. 3) refer to（）

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