Answer the following question given this paragraph: 

Cells are found in all different types of environments, and these environments are constantly changing. For example, one-celled organisms, like bacteria, can be found on your skin, in the ground, or in all different types of water. Therefore, cells need a way to protect themselves. This job is done by the cell membrane, which is also known as the plasma membrane.


Q: Name a one-celled organism that  can be found on your skin, in the ground, or in all different types of water.

 Choices:

- virus

- fungus

- pathogens

- bacteria

A:
bacteria
