Final answer:
An air tank is equipped with a drain valve to remove air and water.
Step-by-step explanation:
The correct answer is A) air and water. An air tank is equipped with a drain valve to remove air and water. This is because when compressed air is stored in a tank, moisture from the air can condense and accumulate as water vapor. The drain valve allows for the removal of both air and water from the tank, ensuring that only clean and dry air remains.