Explanation:

- Conduction: Heat transfer through direct contact. Metals in the kettle base conduct heat, but not the main water heating method in a kettle.

- Convection: Heat transfer through fluid movement. In a kettle, hot water rises and cooler water sinks, creating a circulation that uniformly heats the water.

Correct Answer: Convection

- Radiation: Heat transfer through electromagnetic waves. Doesn't play a significant role in heating water in a kettle.

- Motion of its molecules: Describes kinetic energy increase in water molecules as they heat up, but not a direct method of heat transfer like conduction or convection.