* Sang is the past tense of the verb "sing."
* Example: "She sang a beautiful song."
* Sung is the past participle of the verb "sing." It's used in the perfect tenses (present perfect, past perfect, and future perfect) and in passive voice.
* Example: "He has sung in the choir for years."
* Example: "The song was sung by the entire audience."
So, the correct verb depends on the context.