Which of the following is mentioned as a reason for the low population growth rate?

This week, the United States Census Bureau released its official count of the nation’s population. It said the population, as of April first, was 308 ,745 ,538.(30)The population increased 9.7% in ten years.(29)This was the nation’s lowest growth rate since the 1930s. Experts say this was a result of falling birth rates among some groups and fewer immigrants because of the recession. Two states had the largest population increases.(30)Texas gained more than four million people— more than any other state.(30)Nevada was the fastest growing state. Its population increased thirty-five percent from the last census in 2000.(30)Across the country, the largest increases were in southern and western states. The population continues to move from the Northeast and Midwest to the South and West. This has been happening for the past forty years.