Considering the Parable of the Persistent Widow (Luke 18:1-8), what theological truth about prayer does Jesus emphasize beyond the simple idea of not giving up?

A God only answers prayers that are repeated multiple times. B God's justice, while sometimes delayed, will ultimately prevail for those who trust in Him, and persevering prayer demonstrates that trust. C The effectiveness of prayer depends on the persistence and volume of the requests. D Prayer is primarily a means of convincing God to change His mind.