In the book of Ruth, beyond the love story, what legal and cultural practice does Boaz uphold by marrying Ruth, securing Naomi's family lineage and inheritance?

A The practice of levirate marriage, where a close relative marries a widow to continue her deceased husband's line. B The custom of gleaning, allowing the poor to gather leftover crops from the fields. C The tradition of offering a dowry to the widow's family as compensation for her loss. D The ritual of purification, where the widow undergoes a cleansing ceremony before remarriage.