- Digestion is when stomach acid breaks down food
- The digestive system digests food for the body
- Therefore, the digestive system breaks down food

- If something is made of something else then that something can be broken down into that something else
- If something is made of something else then that something contains that something else
- Hence, if something contains something else then that something can be broken down into that something else

- The digestive system breaks down food
- If something contains something else then that something can be broken down into that something else
- So, the digestive system breaks down food into the substance that it contains

- A body is a part of a living thing
- Food contains nutrients for living things
- So, food contains nutrients for a living thing's body

- The digestive system breaks down food into the substance that it contains
- Food contains nutrients for a living thing's body
- Therefore, the digestive system breaks down food into nutrients for the body

- Nutrients are simpler than food
- Nutrients are a kind of substance
- So, nutrients are a kind of simple substance

- The digestive system breaks down food into nutrients for the body
- Nutrients are a kind of simple substance
- Therefore, the breaking down of food into simple substances occurs in the digestive system

Hence, the breaking down of food into simple substances occurs in the digestive system
Question: In the human body, the breaking down of food into simple substances occurs in the
Context: - Digestion is when stomach acid breaks down food 
- Nutrients are simpler than food 
- A body is a part of a living thing 
- Food contains nutrients for living things 
- Nutrients are a kind of substance 
- If something is made of something else then that something can be broken down into that something else 
- The digestive system digests food for the body 
- If something is made of something else then that something contains that something else