‘Q’ will be the first part of the given sequence as the pronoun ‘it’ is used in relation of ‘the library of a famous divine’ in S1. ‘P’ will follow next as ‘multitudes of the books’ is in the context of ‘rare books’ in ‘Q’. ‘S’ will come next because ‘them’ refers to ‘books had the marks or libraries’ in ‘P’. ‘R’ will come next because it gives a reason for not finding an opportunity to return the borrowed books, that is, he is possessive about the books. Hence, QPSR is the correct sequence. Thus, option (b) is correct.