The polar modulus for a hollow shaft of outer diameter (D) and inner diameter (d) is

• A. <img src="/_files/images/mechanical-engineering/strength-of-materials/109-284-1.png">
• B. <img src="/_files/images/mechanical-engineering/strength-of-materials/109-284-2.png">
• C. <img src="/_files/images/mechanical-engineering/strength-of-materials/109-284-3.png">
• D. <img src="/_files/images/mechanical-engineering/strength-of-materials/109-284-4.png">