Given the task definition and input, reply with output. You are given a paragraph, a question and some answer options (associated with "A", "B", "C", "D", etc.) You need to list all the correct answer options with their associated letters (e.g. "A" can be a valid answer). Note that sometimes, more than one option can answer the question correctly and completely. In those cases, please generate all such options separated by a comma (e.g. "A, B" is a valid answer). Do not generate anything else apart from one or more of the following characters: 'A', 'B, 'C', 'D', etc.

Paragraph- Sent 1: Conduction is the transfer of thermal energy.
Sent 2: It occurs between objects or substances that are touching.
Sent 3: Thermal conductors are materials that are good conductors of heat.
Sent 4: Thermal insulators are materials that are poor conductors of heat.
Sent 5: Both conductors and insulators have important uses.
Sent 6: Convection is the transfer of thermal energy.
Sent 7: This occurs as particles move within a fluid.
Sent 8: The fluid may be a liquid or a gas.
Sent 9: The particles within the fluid transfer energy by moving from warmer to cooler areas.
Sent 10: They move in loops.
Sent 11: These loops are called convection currents.
Sent 12: Radiation is the transfer of thermal energy by waves.
Sent 13: These waves can travel through empty space.
Sent 14: When the waves reach objects, the heat is transferred to the objects.
Sent 15: Radiation is how the Sun warms the Earths surface. 
Question: What is it called when thermal energy is transferred between 2 objects that are touching (A) Convection (B) Conduction (C) Induction (D) Radiation.

B.