Right choice is (a) \(Γ_{xy}=\frac{∂v}{∂x}+\frac{∂u}{∂y} \)
For explanation: In order to find the shearing strain component in X-Y plane, let us consider a plane lamina of size dx, dy in X-Y plane. If u is the displacement in x-direction and v is the displacement in y-direction, the shearing strain component is,
\(Γ_{xy}=\frac{∂v}{∂x}+\frac{∂u}{∂y} \).