Answer: A) change was to were.
Explanation: The subjunctive mood is the verb form used to express a wish, a suggestion, a command, or a condition that is contrary to fact. From the given options, the revision that changes the underlined verb (was) to the subjunctive mood, is the corresponding to option A: change was to were, because the subjunctive form of the verb "to be" is "were." The complete answer would be: If the test were easier, teachers would not know what students really learned.
