Explanation

• The sentence "If he were taller, he would join the basketball team" correctly uses the subjunctive mood.
• In this construction, "were" is the subjunctive form of the verb "to be."
• The subjunctive mood is often used to express hypothetical or unreal situations, wishes, suggestions, or conditions that are contrary to fact.
• In this case, the speaker is presenting a hypothetical condition (if he were taller) and its potential result (he would join the basketball team).
• The use of "were" in the if-clause reflects the unreal or hypothetical nature of the statement, making it an appropriate application of the subjunctive mood.