The centre of gravity of a trapezoidal dam section whose top width is a, bottom width is b and the vertical side is a, from its vertical face is

• A. <img src="/_files/images/civil-engineering/applied-mechanics/116-5.227-1.png">
• B. <img src="/_files/images/civil-engineering/applied-mechanics/116-5.227-2.png">
• C. <img src="/_files/images/civil-engineering/applied-mechanics/116-5.227-3.png">
• D. none of these.