The body circulatory system includes the heart and blood vessels. The heart pumps the bloods to all parts of body through a network of arteries（动脉） and vein.
The digestive system breaks down and absorbs food into the body. It supplies the energy that the body needs for growth and repair. After digestion, excess food is turned into waste and eliminated from the body.
The nervous system includes the brain, spinal cord and nerves. This is your bodies control system. It controls your muscles and organs included your circulatory and digestive system.
The nervous system regulates your heartbeat and digestion.
The respiratory system includes the nose and lungs. It brings air and oxygen into the body and removes carbon dioxide. The lungs are where oxygen enters the bloodstream and carbon dioxide is removed.
The immune system protects the body against infections and diseases. Sneezing and fever are examples of how the immune system works. If an infection invades the body and the immune system attacks it.
The control use of fire allowed people to cook food and survive in the colder climates. Fire provided the light so that people could work and socialize for longer hours.
With the invention of agriculture, people can grow food and settle into communities. By growing food, people could spend less time hunting and more time for other things, such as art.
With the development of agriculture, people had more time for other activities.
The domestication of animals allows people to raise and use animals for food and work. By raise herds of animals, such as sheep, people have regular supply of meat and clothing. The strength of animals such as horses and oxen was used for work and transportation.
The development of tools and machines has resulted in a more fashion manufacturing and construction. With better tools and machines, works can be done with fewer people and much lower cost.
The development of science and engineering has improved many thing including communications. With understanding of electricity, telephone and radios allow people to communicate over long distances.
The use of machines has reduced the number of people needed to make things.
