A tape of length l and weight W kg/m is suspended at its ends with a pull of P kg, the sag correction is

• A. <img src="/_files/images/civil-engineering/surveying/51-3.23-1.png">
• B. <img src="/_files/images/civil-engineering/surveying/51-3.23-2.png">
• C. <img src="/_files/images/civil-engineering/surveying/51-3.23-3.png">
• D. <img src="/_files/images/civil-engineering/surveying/51-3.23-4.png">
• E. .