Choose one right variant. ____ this song many times before.

The sentence describes a past action that occurred multiple times before another past action or a specific point in the past. The past perfect tense is used for this purpose. Therefore, 'had heard' is the correct choice to complete the sentence, indicating a completed action in the past prior to another past event or time. The structure is Subject + had + past participle. The sentence implies a completed action in the past before another past event. The past perfect tense is appropriate here. The correct option is 'had heard'.