<em>The movement of air in a hot air balloon makes it move up into the sky.
</em>
<u>Explanation:</u>
Convection takes place in fluids. Hot fluids are less dense than cold fluids and the difference in the densities determine the direction of flow of fluids. <em>Less dense fluid moves up and the denser fluid take its place. </em>
Thus hot air rises up and cold air fills its place. The hot air balloon contains burner which <em>pumps hot air into the balloon.</em>
Thus the air inside the balloon will be hotter than the air outside the balloon. <em>Thus the hot air rises up carrying the balloon forward.
</em>
B. and E. are the correct answer because convection is the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.
