How Do Living Systems "Know" the Appropriate Temperature or Water

How do living systems "know" the appropriate temperature or water content within that system?

A) Living systems depend on signals from the environment to regulate these conditions.
B) Organisms have a genetically predetermined set point that must be internally maintained.
C) Living systems monitor positive feedback mechanisms and shut off negative feedback loops to regulate these processes.
D) Actually, most living systems do not regulate temperature or water content, so these features typically fluctuate greatly.