A shaft of diameter 'd' is subjected to bending moment 'M' and twisting moment 'T' The developed principal stress will be

• A. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/47-873-1.png">
• B. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/47-873-2.png">
• C. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/47-873-3.png">
• D. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/47-873-4.png">