Answer:
1 cup of milk
Explanation:
If 1/2 cup of milk is needed for 2 cups of chocolate, and you need to find how much milk is needed for 4 cups, then you'd follow the same steps as going from 2 cups to 4, multiplying by 2.
2 cups chocolate x 2 = 4 cups chocolate
1/2 cup milk x 2 = 1 cup