Which plot description is the best example of a tragedy?   a. a puppy gets lost during a cross-country move and experiences many dangerous situations as he finds his way back to his family.   b. a billionaire oilman loses his fortune and his family after he fails to see the damage his company is doing to the environment.   c. an old man recounts his amazing experiences during the war, remembering all of the friends he made as well as those he lost.   d. a young married couple begins to grow apart as work and family obligations take their toll on the marriage, causing them to split up.