An example of natural convection would be
a. placing an ice cube in your hand.
b. the movement of the mantle inside earth.
c. getting warmed by the sun.

the movement of the mantle inside the earth.

The natural convection is a process, in which the fluid movement occurs from heat transfer. When a fluid is warmed or chilled, its density changes and the buoyancy effect create a natural flow in the affected region, which makes itself the rise of hotter fluid and the fall of cooler fluid: hence, energy transfer from hotter area to colder area and such process is repeated as long as the temperature variation in fluid exist.

Mantle convection is the quiet creeping motion of Earth's solid silicate mantle produced by convection currents conveying heat of the inside to the planet's surface.

cellular respiration oxidizes food into energy in the form of atps.

glycolysis (6 c hexose) > 2x atps are used > 6c hexose biphosphate > 2 x 3c triphosphate >

2 x 3c pyruvate (2x nadh produced from nad) and (4x atp produced)

pyruvate actively pumped mitochondrial matrix.

c. is the correct answer