If is the vertical angle of an inclined sight, is the angle of tilt of the staff, the error

• A. <img src="/_files/images/civil-engineering/surveying/62-3.175-1.png">
• B. <img src="/_files/images/civil-engineering/surveying/62-3.175-2.png">
• C. <img src="/_files/images/civil-engineering/surveying/62-3.175-3.png">
• D. none of these.