| What is the operating principle upon which a bubble tube system operates in indicating liquid tank level? |
| A) The air pressure required to force air bubbles into the liquid near the top of the tank is proportional to the liquid level in the tank. |
| B) The air pressure required to force air bubbles into the liquid near the bottom of the tank is inversely related to the liquid level in the tank. |
| C) The air pressure required to force air bubbles into the liquid near the bottom of the tank is proportional to the liquid level in the tank. |
| D) The air pressure required to force air bubbles into the liquid near the top of the tank is inversely related to the liquid level in the tank. |
