The energy stored in a strained wire is given by

• A
  $\frac{1}{2} \times \text{load} \times \text{extension}$
• B
  $\frac{1}{2} \times \text{extension} \times \text{stress}$
• C
  $\frac{1}{2} \times \text{stress} \times \text{strain}$
• D
  $\frac{1}{2} \times \text{strain} \times \text{load}$