The correct option is
C bake
The sentence indicates that the subjects do not buy their bread. Thus, the answer should be an action that can be done to bread but, does not involve buying it.
Option A is incorrect. Although make fits in the blank, it is incorrect because the word 'make' is not generally used to refer to food items. It is usually used for objects that are manufactured. Thus, it is not the best fit.
Option B is incorrect. Cook is also a good fit. Also, cook is used to refer to food. Yet, it is incorrect because 'cook' is very non-specific and can be used to refer to any type of food. Thus, it is not the best fit.
Option C is correct. Bread is a baked product. Baking is the cooking method used to make bread. Thus, it is more specific than 'cook'. Therefore, it is the best fit among the given options.
Option D is incorrect. Bring does not fit in the blank as, in this context it can mean 'buy'. Since we know that the subjects do not buy their bread, option D is incorrect