In stage 1 the two rates are balanced. In stage 2 they diverge , as the death rate falls relative to the birth rate. In stage 3 they converge again, as the birth rate falls relative to the death rate. Finally in stage 4 the death and birth rates are balanced again but at a much lower level.
Nuclear fusion generates the energy that is released by stars.
In the great majority of stars, it's the fusion of hydrogen nuclei
to form helium nuclei plus energy. In very old stars, the nuclei
of heavier elements are fused, forming even heavier ones.
Twilight zone because the twilight zone is the deepest part of the ocean
Yes because rivers are important for trade and even things like fresh water and transport.
