If the strain energy stored per unit volume in a hollow shaft subjected to a pure torque when t attains maximum shear stress fs the ratio of inner diameter to outer diameter, is

• A. <img src="/_files/images/civil-engineering/theory-of-structures/89-21-94-3.png">
• B. <img src="/_files/images/civil-engineering/theory-of-structures/89-21-94-4.png">
• C. <img src="/_files/images/civil-engineering/theory-of-structures/89-21-94-2.png">
• D. <img src="/_files/images/civil-engineering/theory-of-structures/92-21-125-4.png">