In the Parable of the Persistent Widow (Luke 18:1-8), what is the primary theological point Jesus is making about prayer?

A God only answers prayers after repeated requests. B God is unjust and needs to be persuaded through relentless supplication. C Believers should always pray and not give up, trusting that God will ultimately bring justice and answer their prayers, even if it seems delayed. D Prayer is primarily about wearing down God's resistance through sheer persistence.