Answer the following question given this paragraph: 

The nervous system is a complex network of nervous tissue that carries electrical messages throughout the body. Its functions include controlling muscles, maintaining balance, sensing internal and external environments, controlling body systems to maintain homeostasis, preparing the body for emergencies, and allowing higher mental functions such as thinking.


Q: Which human body system is a complex network of nervous tissue that carries electrical messages throughout the body?

 Choices:

- the localized system

- the lymph system

- the bacterial system

- the nervous system

A:
the nervous system
