In the Parable of the Sower (Matthew 13:1-23), what does the seed that falls on rocky ground primarily represent?

A Those who initially receive the word with joy, but fall away when faced with hardship or persecution. B Those who hear the word but do not understand it. C Those who hear the word and produce a bountiful harvest. D Those who are too preoccupied with worldly concerns to pay attention to the word.