Homeostasis can occur at the cellular level or the system level.
a. true
b. false

This is true. Homeostasis is a very broad concept that can encompass not only a systems level approach but also the celullar level. When you have a irregularity at the cellular level (Having too many ions of some sort somewhere in one cell), this presents a deviation from homeostasis at the cellular level. When you're observing a deviation in the form of a higher body temperature, this is a deviation at the systems level. 

Cbecause it is the only one describing a habitat