7. which statement best describes the source of the sun's energy?
a. hydrogen fuses to form helium.
b. protons merge with electrons to form neutrons.
c. oxygen combines with elements in the sun.
d. the high temperature of the photosphere produces radiation.

the answer is :

imagine a line passing through the center of earth that goes through both the north pole and the south pole. this imaginary line is called an axis. earth spins around its axis, just as a top spins around its spindle. this spinning movement is called earth's rotation. at the same time that the earth spins on its axis, it also orbits, or revolves around the sun. this movement is called revolution.