GRE General Test: SE-335756 GRE Sentence Equivalence

If he had not had the _____ to follow his own iconoclastic theories in the face of the apparently unassailable conclusion of the accepted experts in the field, progress would have been inestimably slower in this area of knowledge.
Select the two answer choices that, when used to complete the sentence, fit the meaning of the sentence as a whole and produce completed sentences that are alike in meaning