Which type of heat transfer occurs through electromagnetic waves? A. insulation B. conduction C. radiation D. convection

C is radiation
Convection is the transfer of heat by the flow of material (usually air or water)
Conduction is energy transferred when molecules bump into one another
Radiation is the answer

Electromagnetic waves are often called "electromagnetic radiation".
That's a really strong clue.

Heat carried in the form of electromagnetic waves is radiation.