Answer:
The looming national debt is a major problem in the United States that will have untold impact on society.
Explanation:
This is the best thesis statement in the options you have provided as one, it addresses the main topic which is the national debt, while the other 3 talk about the national debt with out actually saying that it is about the national debt. For an example if you had to chose , "the dog is fast Ā or "he is fast" for the thesis statement you should pick "the dog is fast" as it addresses what your talking about. Hope this helps if you have another question comment it.