Final answer:
The integer 0 represents the reference point for measuring the airplane's height.
Step-by-step explanation:
The integer 0 in this context represents option c) The reference point for measuring the airplane's height. When the height of the model airplane is measured, 0 represents the starting point or reference point for the measurement. Any positive value above 0 represents the height above the ground, while any negative value below 0 represents the depth or distance below the ground.