Two 20 kg blocks are connected by a 2.0-m-long, 5.0-mm- diameter rope. Young's modulus for this rope is 1.5 X 10⁹ N/m². The rope is then hung over a pulley, so that the blocks, hanging from each side of the pulley, are in static equilibrium. By how much does the rope stretch?

A. 3.0 mm 

B. 6.3 mm

C. 9.3 mm 

D. 13 mm