Answer the following question given this paragraph: 

Convection is the transfer of thermal energy by particles moving through a fluid. Particles transfer energy by moving from warmer to cooler areas. That’s how energy is transferred in the soup in Figure above . Particles of soup near the bottom of the pot get hot first. They have more energy so they spread out and become less dense. With lower density, these particles rise to the top of the pot (see Figure below ). By the time they reach the top of the pot they have cooled off. They have less energy to move apart, so they become denser. With greater density, the particles sink to the bottom of the pot, and the cycle repeats. This loop of moving particles is called a convection current .


Q: Convection is the transfer of thermal energy by particles moving through what?

 Choices:

- Solid

- tissue

- Metal

- fluid

A:
fluid
