http://www.engvid.com/ "The leg of the dog" or "the dog's leg"? "England's role" or "the role of England"? "Almost all students" or "almost all of the students"? In this lesson, I'll teach you when to use the preposition 'of'. Although it's a small word, mastering 'of' is a challenge for many students. Let's solve the mystery of the word 'of' together.