This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to use leftover roast
Make beef broth.
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.

- 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.
- 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.
- 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.
- Allow the beef broth to cook on low heat. You can substitute sherry vinegar if you'd prefer a sweeter flavor.
The answer is:
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.