How do astronomers know that dark matter exists? A. Because it emits electromagnetic radiation
B. Because it can be directly observed
C. Because its gravity affects the motion of objects around it
D. None of the above

C. Because it's gravity affects the motion of objects around it.

answer; the correct answer is (beta)

the most common energy conversion is from kinetic energy to potential energy, and then from potential energy to kinetic energy.

later on comes the heat energy, mechanical energy, and other energy conversions.

this energy conversion is so common that we can find it in our day to day lives as well.

- one of the most common energy conversions involves the changing of potential energy to kinetic energy or kinetic energy to potential energy