This page shows a few sample books that may be helpful to complete the last assignment:
Describe of one of the Zoroastrian purification rituals, or one of the Zoroastrian practices relating to purity.
Then, compare the Zoroastrian ritual or practice of your choice with a ritual or practice relating to purity of another religion.
Notes: I strongly recommend checking the Oxford Bibliographies page because it has far more resources than this page (e.g., Biblical Studies, for example, offer a number of recommended resources.)
When you see Call Numbers, this means that a physical copy is available.