Answer the following question given this paragraph: 

The type of chemical signal a cell will send differs depending on the distance the message needs to go. For example, hormones , ions, and neurotransmitters are all types of signals that are sent depending on the distance the message needs to go. Endocrine signals are hormones, produced by endocrine organs. These signals travel through the blood stream to reach all parts of the body.


Q: Hormones, ions, and neurotransmitters are all types of what?

 Choices:

- nutrients

- pathogens

- proteins

- chemical signals

A:
chemical signals
