If is the angle of deflection of a simple curve of radius R, the distance between the mid-point of the curve and long chord, is

• A. <img src="/_files/images/civil-engineering/surveying/63-3.188-1.png">
• B. <img src="/_files/images/civil-engineering/surveying/63-3.188-2.png">
• C. <img src="/_files/images/civil-engineering/surveying/63-3.188-3.png">
• D. <img src="/_files/images/civil-engineering/surveying/63-3.188-4.png">
• E. .