Why must the chemical make up of food be changed?

If you are referring to digestion...

Well your body cannot take in food as is because your body cannot absorb it. What digestion does is it actually picks out what the body can take in and gets rid of everything else that cannot pass through the mucosa (lining of the digestive tract).

Aside from this, your body actually uses food as a source of nutrients that are needed for your different cells to function. So the digestive system transforms it into a form that the cells of your body can use to perform their function. Many of these nutrients are used for not only maintaining the organs but for repair and replacement too.

sadly i believe the answer is d