Answer:
D. blowing on the hot cocoa to cool it is the correct answer.
Step-by-step explanation:
Convection can be defined, according to the Cambridge Dictionary, as "the flow of heat through a gas or a liquid as the hotter part rises and the cooler part falls." In this case, the hot cocoa is getting cooler as cool air arrives to the hot cocoa and the steam caused by it rises. Due to this, D is the correct answer.