Let angular value of one graduation of a tube of length x be seconds and R be the radius of its internal curved surface, then

• A. <img src="/_files/images/civil-engineering/surveying/54-3.68-1.png">
• B. <img src="/_files/images/civil-engineering/surveying/54-3.68-2.png">
• C. <img src="/_files/images/civil-engineering/surveying/54-3.68-3.png">
• D. <img src="/_files/images/civil-engineering/surveying/54-3.68-4.png">
• E. .