How is energy transferred by convection?

what are convection currents?

Convection is transferred by mass motion of a fluid such as air or water when heated fluid is caused to move away from the source of heat, carrying energy with it. Convection above a hot surface occurs because hot air expands, becomes less dense, and rises.

Explanation:

A current in a fluid that results from convection.

51% were unhappy, i think .   ; )

even though you have attached neither the chart nor the generalizations, i have located them online. the right answer is d, since they are asking you about a generalization. you can only infer from the chart that between 2008 and 2009 the number of employed workers decreased significantly (from over 115 millions to 107 millions approximately), which signals some type of economic crisis.