Final answer:
The correct answer is 2) Births to single women have declined significantly.
Step-by-step explanation:
The correct answer is 2) Births to single women have declined significantly. In recent years, the rate of cohabitation has increased significantly, which means more couples are choosing to live together without getting married. Additionally, the age at first marriage has increased significantly for both men and women, as more people prioritize education and career before settling down. However, births to single women have not declined significantly and continue to be a trend in the US.