Heat transfer within a fluid takes place by

a.

convection currents.

b.

radiation.

c.

conduction.

d.

density.

I think it's A

Heat transfer within a fluid takes place via convection process. The heated molecules rise up and the cold molecules flow downwards. Hence there is a constant exchange of heat taking place between the molecules within the fluid. The warmer part of the liquid is obviously lighter than the colder part of the liquid and hence it tends to move upwards. There is a constant flow of current between the warmer fluid and the colder fluid and this result in convection current among the molecules.