In levelling operation

ANS:E - both (b) and (c).

The given answer is absolutely right, first reading means the back sight-reading, so when the first reading (back sight-reading) is more than the second reading (foresight reading) it represents a rise and vice versa for fall. For the same set up of instrument, staff reading is more at a lower point (depression) and less for a higher point (hill). Thus, staff reading provides information regarding the relative rise and fall of ground points. This provides the basics behind rising and fall method for finding out the elevation of unknown points.

In above given all options explain wrongly:

* Second reading more than first -fall.
* First reading is more than second-fall.
* First reading is less than second-rise.
* Second reading is less than first-rise. For example:

You took Back sight reading on staff A (imagine it was 1. 6 m) then you took foresight reading on staff B (Imagin it was 1. 8m). It means your staff B is in depression area because it shows more reading as compared Staff A through the instrument.

So if B. S level is less than F. S it means RISE.

And if B. S level is more than F. S it means FALL. B and C are correct because if the instrument is sighted to A and B from the same position then if the staff reading of A is higher than B then it shows that A is in lower elevation because the staff at A will be at the position lower than that of B.

So from the same instrument, the reading of A will be higher.