Statements: Every book on the top shelf is a reference book. No reference book can be taken out of the reading room. Anil took a book out of the reading room. Which of the following must be true?

If the book had come from the top shelf it would be a reference book, and no reference book can leave the reading room. Since Anil did take it out, the book was not a reference book and so cannot have come from the top shelf. The second option reverses the first statement, and the fourth is contradicted by his presence there.