Heat from the surface is transferred underground by

a.) convection
b.) condensation
c.) radiation
d.) conduction

Option (D) is the correct answer.

Explanation:

When we place two objects of different temperature adjacent to each other then there will occur transfer of heat from hotter object to colder object till their temperature becomes equal.  

This process is known as conduction.

Hence, when heat is being transferred from surface to the underground then it is due to the process of conduction.

Convection is defined as the process in which a fluid (liquid or gas) when heated then more dense (cooler) substance sinks ate the bottom whereas less dense (hotter) substance will rises at the top. Radiation is defined as a process in which an electromagnetic energy will travel through space in the form of waves or particles.Condensation is a process in which vapor state of a substance changes into liquid state.

Thus, we can conclude that heat from the surface is transferred underground by conduction.