What is the primary role of subjunctive mood in sentences?

The primary role of the subjunctive mood in sentences is to express ideas that are contrary to fact. This mood is used to convey situations that are hypothetical, wished for, or not currently true. For instance, in the sentence "If I were a bird, I would fly high," the use of "were" indicates a scenario that is not true in reality, emphasizing a wish or a fictional situation.

The subjunctive can also be employed in contexts involving doubt, uncertainty, or necessity, which further illustrates its ability to reflect non-factual states or desires. For example, one might say, "I wish it were sunny," which indicates a desire for a condition that is not presently the case. This specific function – to denote unreal or imagined circumstances – distinguishes the subjunctive mood from other grammatical moods that express certainty or reality.

Therefore, option C accurately captures the essence of how the subjunctive mood functions within sentences.