Are there different version?

I downloaded the Hooktheory I book from iBooks. My professor assigned reading from the first three sections: The Building Blocks of Music, Relative Notation and Chords. however, my book starts with The Major Scale. Are there different versions or am I missing something?

@badasci96 this is the right version. The book is available on multiple platforms (web, iphone, android, etc.) but the content is the same. Keep reading :-). It starts with the major scale but quickly gets to the other concepts you mentioned.