It's a bit tricky to answer what the "main" three parts of the human body are, as it depends on how you define "main". Here are a few ways to break it down:

1. Based on Major Systems:

* Nervous System: This controls everything from your thoughts and senses to your movements and breathing.

* Circulatory System: This carries blood, oxygen, and nutrients throughout your body.

* Digestive System: This breaks down food and absorbs nutrients.

2. Based on Anatomy:

* Head: This houses the brain, face, and senses.

* Torso: This includes the chest, abdomen, and back, containing vital organs like the heart and lungs.

* Limbs: This includes the arms and legs, which allow for movement and interaction with the environment.

3. Based on Function:

* Support System: This includes your skeleton, muscles, and tendons, providing structure and allowing movement.

* Control System: This includes your brain, spinal cord, and nerves, regulating all bodily functions.

* Maintenance System: This includes your digestive, circulatory, respiratory, and excretory systems, responsible for keeping your body healthy and functioning.

Ultimately, there's no single "right" answer to the question of the main three parts of the human body. It depends on what aspect you're focusing on!