Which of the answers took up the largest percentage of U.S. spending in the 2016 budget?

The correct answer is C. healthcare.

In the 2016 U.S. budget, healthcare accounted for the largest percentage of federal spending. This includes costs for programs like Medicare and Medicaid, which are significant expenditures in the federal budget, surpassing those for transportation, welfare, and education. If you’d like more detailed information or further assistance, feel free to ask!