The independent clause in the sentence is "we returned it." This is the answer because if you say the sentence alone it makes since and it does not need another sentence to support it. Furthermore, the dependent clause in that sentence is "Because the shirt had a tear,". This does not express a reasoning for the shirt having a tear. But, "we returned it", has a subject and a verb. "we" is the subject, and the action of returning is the verb. I hope this has been helpful. : )