______________________________ to keep his promise, he will earn the distrust of all the voters.

(I) If the candidate has failed

(II) Since the candidate has failed

(III) If the candidate fails

Both the phrases “Since the candidate has failed” and “If the candidate fails” can substitute the given blank to make the sentence grammatically correct and contextually meaningful. It is to be noted that the sentence is conditional. So the correct syntax is [If+S+V1, S+will+V1]. Hence 3 is the correct option.