A

To determine the relation between stress and strain for an elastic material, we refer to Hooke's Law, which states that the stress is proportional to the strain in a linear elastic material. This is mathematically represented as:
$$ ext{Stress} (\sigma) = E \cdot \text{Strain} (\epsilon) $$
where \(E\) is the modulus of elasticity (Young's modulus).
In the context of the options provided, Option A represents this relation with the form of the equation similar to Hooke's Law, confirming that it is the correct answer.