The distance of the c.g. of a semi-circular arc of radius r from its diameter along the radius of symmetry, is

• A. <img src="/_files/images/civil-engineering/applied-mechanics/116-5.231-1.png">
• B. <img src="/_files/images/civil-engineering/applied-mechanics/116-5.231-2.png">
• C. <img src="/_files/images/civil-engineering/applied-mechanics/116-5.231-3.png">
• D. <img src="/_files/images/civil-engineering/applied-mechanics/116-5.231-4.png">