Considering the historical context of the book of Ruth, what significant social custom is highlighted in the story when Boaz redeems Ruth and Naomi's land?

A The concept of a kinsman-redeemer, ensuring family property and lineage are preserved. B The tradition of gleaning, allowing the poor to gather leftover crops from fields. C The custom of offering hospitality to strangers, providing them with food and shelter. D The practice of levirate marriage, which was not directly applied in Ruth's case.