In leveling operations, a line is established between two points to determine the difference in elevation between them. This process involves taking measurements using a leveling instrument, such as a level or a theodolite.

The correct answer is option 'c) The line commences with a back sight and closes with a foresight.'

Explanation:

1. Back Sight:
- The back sight is the first reading taken on a point of known elevation, such as a benchmark or a previously established point.
- It is called a back sight because it is taken with the instrument placed at the back of the point.
- The purpose of the back sight is to establish a starting reference point for the leveling process.

2. Intermediate Sight:
- After taking the back sight, the leveling line is extended to the next point.
- The next reading taken on this point is called an intermediate sight.
- The intermediate sight is used to continue the leveling line and determine the difference in elevation between the two points.

3. Change Point:
- The intermediate sight is taken on a change point, which is a point where the elevation changes along the line.
- Change points can be natural features such as ridges or valleys, or they can be man-made features like roads or buildings.
- The purpose of taking an intermediate sight on a change point is to determine the difference in elevation between the two points on either side of the change.

4. Fore Sight:
- After taking the intermediate sight on the change point, the leveling line is extended further to the next point.
- The next reading taken on this point is called a fore sight.
- The fore sight is taken with the instrument placed in front of the point.
- The purpose of the fore sight is to determine the difference in elevation between the change point and the next point.

5. Closing the Line:
- The leveling line continues in this manner, with back sights, intermediate sights, and fore sights, until the desired points are connected.
- The line is closed when a fore sight is taken on the last point, which is typically a benchmark or a known elevation point.
- Closing the line allows for the accuracy of the leveling measurements to be checked and adjusted if necessary.

Therefore, in leveling operations, the line commences with a back sight and closes with a foresight. This sequence of readings ensures that the elevation differences between the points are accurately determined.

In the first option a:to fix the new station point we need to know the know RL of staff.
option B:to carryout the levelling we need to shift the staff in the line of surveying.