Correct grammar. Change 'The' to 'They'

_posts/1900-01-05-them-what.md

@@ -2804,7 +2804,7 @@ already have. It seems like it should work by itself.”
 
 Dr. Cham looked up from the keyboard at the goat. “Well, it’s sort of like your
 video collection. None of your video cassettes work unless they are put in a
-machine that uses video cassettes. The depend on each other. A mixin has some
+machine that uses video cassettes. They depend on each other. A mixin has some
 basic requirements, but once a class meets those requirements, you can add all
 this extra functionality in.”