Although the options are not included with the question, we can still look at how this conflict develops the plot.
The king is in love with Perseus' mother, Danae, but Perseus does not think he is worthy of her. I order to get him out of the way, the king asks Perseus for the head of Medusa. He is only using this as a ploy to get his mother. The conflict enhances the excitement of the story and develops the plot, as it makes the reader wonder whether Perseus will be able to achieve this feat.