Final answer:
The majority of the discretionary budget is spent on defense, education, and healthcare. Social Security is part of mandatory spending, not discretionary.
Step-by-step explanation:
The plurality of money in the discretionary budget is primarily spent on defense, and a significant portion is also dedicated to education and healthcare. According to the information provided, in the 2015 discretionary budget defense received the largest allocation at over 50%, with education and healthcare also receiving notable but smaller appropriations. It's important to note that Social Security and welfare are primarily part of mandatory spending, which is separate from the discretionary budget that Congress authorizes annually.