The elastic potential energy of a strained body is

• A
  $\frac{1}{2} \times \text{stress} \times \text{strain}$
• B
  $\frac{1}{2} \times \text{stress} \times \text{strain} \times \text{volume of the body}$
• C
  $\frac{1}{2} \times \text{stress} \times \text{strain} \times \text{area of the body}$
• D
  $\text{stress} \times \text{strain} \times \text{volume of the body}$