The correct answer is D. all of the above.
The rise and fall method of levelling is a technique used in surveying to determine the difference in elevation between two points. The method involves taking a series of measurements, called sights, from a known point to an unknown point. The difference between the backsight and foresight is the rise or fall of the ground between the two points.
The rise and fall method provides a complete check on all of the sights taken. This is because the difference between the backsight and foresight must be equal to the sum of the intermediate sights. If the difference is not equal, then there is an error in one or more of the sights.
The backsight is the first sight taken when levelling. It is taken from a known point to an unknown point. The foresight is the last sight taken when levelling. It is taken from an unknown point to a known point. The intermediate sights are the sights taken between the backsight and foresight.
The rise and fall method is a very accurate method of levelling. It is used in a variety of applications, such as construction, surveying, and engineering.