If a circular beam of diameter d experiences a longitudinal strain and a lateral strain the volumetric strain is

• A. <img src="/_files/images/civil-engineering/strength-of-materials/136-6.172-1.png">
• B. <img src="/_files/images/civil-engineering/strength-of-materials/136-6.172-2.png">
• C. <img src="/_files/images/civil-engineering/strength-of-materials/136-6.172-3.png">
• D. <img src="/_files/images/civil-engineering/strength-of-materials/136-6.172-4.png">
• E. none of these.