Choose all correct statements that describe the primary purpose or functionality of unsupervised domain adaptation (UDA).
1. It reduces the theoretical lower bound of the target error by aligning source and target feature distributions.
2. It assumes that labels from both the source and target domains exist.
3. No answer.
4. It uses only data from the source domain to train the model.
5. It adapts a model to a new domain without using any labels from the target domain.