I can't imagine what A and B would contribute to life expectancy.
C is a bit of a different choice. It would, I think, decrease the life expectancy of the general population depending on which country is allowed to come into America.
The best answer to an increased life expectancy would be D. It is certainly true.
D <<<<< Answer
<span>the Great Society is one big thing so pick that</span>
The answer is agriculture
No opinion is in the thesis statement. You are try to get the point across. Make sure it clear too.