Which of the following is an example of homeostasis?
ingesting too much alcohol leads to vomiting.
tapping the knee with a hammer results in the leg suddenly kicking.
darkening a room makes it easier to sleep.
sleeping leads to dreaming.

Option A.

Explanation:

Homeostasis can be defined as the condition of organism that regulates and maintains the internal body variation with respect to external environment such as body temperature and fluid balance.

The process of homeostasis can be well explained by the example of vomiting lead by ingesting too much alcohol. Our body can withstand a certain amount of toxins, when body consumes too much alcohol, body feels it as unhealthy or toxic and to regulate body system, it rejects an overload of poison to the system that leads to vomiting.

Hence, the correct of option is A.