Lesson 19 covers the adjective clause when applied to humans (who, whose, whom), and Lesson 20 presents the adjective clause for non-humans (which, that).There are many topics that pop up, such as when to use them, how to use them, and where to put them, but you'll find it all covered here. One interesting classroom technique appears with Exercise A. It involves merging two sentences by turning one of them into an adjective clause. What is to be removed? What replaces it? Where should you put it