Most contestants believe that the voting system, which we've been using for twenty years, ______ fair.
Which of the following options correctly completes the sentence above?

Question

Quizplus · Accepted Answer

A subject must agree with its verb in number. The subject in this sentence (the voting system) is singular, so we need a singular verb (is).
The use of the verb "were" would require a plural subject. 
The use of the verb "were" would require a plural subject. 
The use of the verb "be" in the sentence does not make sense.

Most Contestants Believe That the Voting System, Which We've Been