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 expenditures accounted for a significant portion of government spending, largely due to programs like Medicare and Medicaid. This spending represents a growing trend in the budget as healthcare costs continue to rise. If you have more questions or need further clarification, feel free to ask!