Step 1: Understanding the formula for energy stored in a capacitor.
The energy stored in a parallel plate capacitor is given by:
\[
U = \frac{1}{2} \epsilon_0 E^2 A d
\]
Where:
- \( E \) is the electric field,
- \( A \) is the area of each plate,
- \( d \) is the distance between the plates,
- \( \epsilon_0 \) is the permittivity of free space.
Thus, the correct answer is (B) \( \frac{1}{2} \epsilon_0 E^2 A d \).