在图书馆偶然发现这本绝版书真是意外的幸运。

Finding this out-of-print ___book in the library was a ___serendipitous discovery.

她在旧书店偶然发现了一本绝版书，真是意外的幸运。

She made a ___serendipitous find of an out-of-print book in the used bookstore.