Statements: No book is a pen. All pens are pencils. Conclusions: I. Some pencils are not books.
II. No pencil is a book. Which conclusion(s) follow?

All pens are pencils and no book is a pen, so those pencils that are pens are not books — thus some pencils are not books, and I follows. Other pencils could still be books, so II is not certain. Only I follows.