If n is the ratio of internal and external diameters of a hollow shaft, the ratio of the weight of the hollow shaft and that of solid shaft of same strength, will be

• A. (1 - n²)/(1 - n²)1/2
• B. (1 - n²)/(1 - n 4 )2/3
• C. (1 + n 3 )/(1 + n 4 )1/2
• D. (1 + n 1 )/(1 + n 4 )2/3