Q1: Determining the difference in elevation between two points on the surface of the earth, is known as

ANS:C - differential levelling

This is the method used in order to find the difference in elevation between two points on the surface of the earth is called differential levelling.  the definition of simple levelling is the process of determining the difference between two points by setting the instrument between them. Because the two points leveling not same. So the elavation difference will come. That is known as differential leveling.