If and be the elevations of two objects A and B respectively, be the angle observed by a sextant. The correct horizontal angle is

• A. <img src="/_files/images/civil-engineering/surveying/74-3.331-1.png">
• B. <img src="/_files/images/civil-engineering/surveying/74-3.331-2.png">
• C. <img src="/_files/images/civil-engineering/surveying/74-3.331-3.png">
• D. none of these.