It would be letter A which is energy. The other three are used in weather forecasting due to the fact that the atmosphere is fluid and weather and climate is caused by uneven heat from the star in our solar system which is the Sun to the Earth in which heat transfer occurs
I'd say B and D definitely, and also E but I'm not entirely sure about that
A net population decline resulting from an "excess of deaths over births".
Option: A
<u>Explanation</u>:
Demographic transition is a shift from higher to lower level of fertility and mortality.Rapid development in industrialization and urbanization in
century resulted into enormous population growth. But decline in early
century covered many reasons like consequences of two calamitous wars, where Europe suffered large population declination due to battle death and civilian causalities in World War I and II. Hence the acceleration of population growth in 19th century but downfall in 20th is also considered as balance.
C. Noth Korea. This country is still a Communist and have a lot of problems in the country.