Answer:
Among the options given on the question the answer is option C.
rising life expectancy
Explanation:In the early 20th century the United States was experiencing the decline of birth rate. There were many reasons behind this. Like as world war I, the Great depression effect in the economy. But after world war II, USA experienced a great increase in the birth rate during the period of 1946 to 1964. This period is called as the Baby Boom in the history of USA. By the end of 1964, 76.6 million babies were born during the period of baby boom.
There are many reasons behind this massive increase of birth rate. Life expectancy was one of the main reason behind this. The strengthened economical condition of the USA has increased the facilities of the people. As a result couples were more willing to have babies.
Moreover soldiers returned from the world war were given the opportunity of job and social securities.As a result they got married inthe pursue of better and fulfill life. 2.2 millions couple were married in 1946 and most of them were strongly inspired to have baby to accomplish the family.
So it can be said that rising life expectancy was a factor behind the Baby Boom.