The most money from a state's treasury is spent every year on what?
politicians' travel
social services
public works
education

'public works' would be the correct answer, public debts are paid off, or contributed towards, there are many issues such as public electricity etc. that is paid for, there are many small (or large) remodeling that is done, grass plantings in public places etc. There is so much to public works, which the other options just have a few things that need paid, public works has many.