Step 1: Understanding the Question:
This question tests knowledge of volume table construction in forest mensuration.
Step 2: Detailed Explanation:
Volume tables applicable to large areas are based on at least two variables.
The two variables are usually diameter at breast height (DBH) and height.
These are the most common variables used in volume estimation.
Single variable tables (A): Used for local areas.
Three variables (B) and four variables (C): Not commonly used.
Thus, the correct answer is two variables.
Step 3: Final Answer:
Thus, volume tables applicable to large areas are based on at least two variables, which corresponds to option (D).
[0.5cm]