The correct answer is C. One must be able to distinguish a thesis from an opinion. D. ("it is morally wrong for any political movement to use violence to achieve its goals") is a subjective point of view that guides his argument, but in and of itself cannot be proved. A. and B. are facts which support his thesis: the rash of violence that swept over France and the French Revolutionary Wars are historical facts not subject to debate (though their evaluation is, of course, subject to debate). His thesis (that is, the argument he is making based on facts) is C. "the French Revolution produced far more negative outcomes than positive ones." Though the thesis is informed by his opinion (D.), a thesis can be proved or at least strongly supported by evidence, while an opinion is generally seen as a matter of belief.