The answer is A, the tendency of a cell to maintain a stable internal environment.
One of the example of homeostasis in human is the control of blood glucose level. If there's too much glucose in our blood, our body release a hormone called insulin to lower the glucose level, to maintain a stable level. On the other hand, if our blood glucose level is too low, another hormone called glucagon is released to raise the glucose level in our blood.
Homeostasis does not only happen to humans, but also to other animals and plants too.
