It would be a. "We the people of the United States ... do ordain and establish this Constitution for the United States of America."
We can rule out c immediately, because it has dependent clauses standing on its own. B. can also be ruled out, because the clause in-between the hyphen does not read correctly. A. is correct grammatically, but D. is also grammatically correct and it explains it in a quick and understandable way.
I think its a tell me if im wrong
