Which of the following events may be a result of a new, fatal disease that affects only senior citizens?

a decline in the birth rate
a narrow band at the bottom of an age structure diagram
an increase in the birth rate
an increase in the death rate of post-reproductive individuals

an increase in the death rate of post-reproductive individuals

Explanation:

In older age the body looses the immunity and the body becomes incapable to fight against the fatal diseases. This results in the increase in the death rate world wide. Death rate can be defined as the the ratio of deaths in a population of a particular area in a concerned time.

An increase in the death rate of post-reproductive individuals is the correct option because senior citizens also belong to post-reproductive age and due to lack of immunity the chances of getting affected by the fatal disease are possible.  

i believe the answer is snake.

it should be d) transitional fossils.

they show the gradualism of evolution throughout a period of time