Step 1: The Prismoidal formula is the most accurate method for computing earthwork volume, as it considers curved surface variations.
Step 2: The formula is:
\[
V = \frac{L}{6} \left( A_1 + 4A_m + A_2 \right)
\]
where:
- \( A_1 \) and \( A_2 \) are the areas of two cross-sections,
- \( A_m \) is the mid-section area,
- \( L \) is the length between cross-sections.
Step 3: The trapezoidal rule is simpler but less accurate, as it assumes a linear variation.
Thus, the correct answer is (D) Prismoidal formula.