The Form of Hooke's Law Relating Shear Stress to Shear $\Delta$

The form of Hooke's law relating shear stress to shear strain is F/A = E $\Delta$ s/h.The figure shows a block subjected to shear stress. Which number corresponds to the surface area A in the equation just given?

A) 1
B) 2
C) 3
D) 4
E) 5