A lively discussion on how best to expose teenagers to the world's dark and disturbing realities became a prevailing defense of a classic novel taught in sophomore English at Douglas High School.On Monday night, a committee of educators, parents and one student voted unanimously, 7-0, to keep Chinua Achebe's African novel, “Things Fall Apart,” in the classroom as part of the SpringBoard curriculum.“To enlighten is to teach,” said Douglas High English teacher Elizabeth Tully. “It is to shine a light on the darkness so that we may improve. I feel the author does that in this book. He wanted to …