The main difference between ponds and lakes is that ponds
a. are inland bodies of water
b. do not develop self-contained ecosystems
c. are smaller than lakes
d. have easily observed currents

c. are smaller than lakes. Ponds and lakes are often indistinguishable, and rules in classifying may differ per region. But ponds are relatively smaller than lakes and more shallow. Lakes are deep  enough that light cannot penetrate the bottom of the water.

The answer is energy. the arrows are showing how exited and energized the stones are.

In fact it is not just nuclear fusion and fission that  can  transform  matter  (or mass)into energy. any time  energy  is produced, some small amount of  matter  or mass isconverted into energy.