The elderly population in the us is expected to increase substantially over the next twenty years. which of the following best explains this population increase?

The us elderly population will increase at a substantial rate of 3.6% over the next 20 years.

Explanation:

This is due to high facilities of medical aid along with low mortality rates especially that of the females is expected to grow more in the future from age of 50 onwards. And continues to remain that way up to 90 years of age according with the population pyramid and sex ratio of the nation. Becoming more of a bell shaped structure.

iii. and iv. only is the right answer