In the Old Testament, the practice of gleaning, as permitted in fields and vineyards, primarily served what purpose within the social structure of ancient Israel?

A To provide a source of income for landowners by maximizing crop yield. B To ensure that all citizens had equal access to land ownership and agricultural resources. C To offer a means of sustenance for the poor, widows, and orphans, reflecting God's concern for the vulnerable. D To promote competition among the working class and encourage individual initiative.