Definition: In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D".
Input: [header] How to use leftover roast [title] Make beef broth. [step] You can make a rich beef broth to have on its own or use the broth as a base for soups and stews. To make the broth, just saute large pieces of the leftover roast beef along with one diced onion. <sep> (A) [substeps] Heat the beef broth in a slow cooker, or just put the onions in with it. Cook the beef broth in the slow cooker for four hours, stirring constantly. (B) Make sure you submerge the beef pieces in a quart of water to make the broth. Leave the meat in the broth for at least one hour and then take it out, rinse, and dry with a small amount of water and store it. (C) Once the onion is soft, add enough water to cover the meat. Bring this to a light boil and keep cooking until the water darkens. (D) Allow the beef broth to cook on low heat. [substeps] You can substitute sherry vinegar if you'd prefer a sweeter flavor.
Output:
C