A section of a solid circular shaft with diameter D is subjected to bending moment 'M' and torque (T). The expression for maximum principal stress at the section is

• A. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/55-347-1.png">
• B. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/55-347-2.png">
• C. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/55-347-3.png">
• D. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/55-347-4.png">