If d and n are the effective depth and depth of the neutral axis respectively of a singly reinforced beam, the lever arm of the beam, is

• A. d
• B. n
• C. <img src="/_files/images/civil-engineering/rcc-structures-design/69-13-5-3.png">
• D. <img src="/_files/images/civil-engineering/rcc-structures-design/69-13-5-4.png">
• E. <img src="/_files/images/civil-engineering/rcc-structures-design/69-13-5-5.png">