Final answer:
Option D is correct, as winter in the story brings about new challenges and conflicts for the protagonist cat to face, making survival more difficult and adding complexity to the plot.
Step-by-step explanation:
In the story How a Cat Played Robin Crusoe, the effect of winter on the plot is best described by option D) Winter creates new conflicts that the cat must now face. This choice reflects the challenges that the cold season typically brings in narratives. For instance, winter often signifies hardships such as scarcity of food and harsh living conditions which create a survival challenge for characters. In the story, this would mean the protagonist cat has to adapt and find new ways to overcome these struggles, adding tension and complexity to the storyline.