In the Parable of the Sower (Matthew 13), what does the seed that falls on rocky ground represent?

A Those who hear the word and immediately receive it with joy, but have no root and endure only for a while. B Those who hear the word, but the worries of this life and the deceitfulness of wealth choke it, making it unfruitful. C Those who hear the word and understand it, and produce a crop, yielding a hundred, sixty or thirty times what was sown. D Those who hear the word, but do not understand it, and the evil one comes and snatches away what was sown in their hearts.