Anovel differs from a short story because it
a. includes a theme.
b. is told as a third-person narrative.
c. is more likely to include subplots.
d. comprises rising action, a climax, and falling action.

B. Is more likely to include subplots.

Short stories (most stories) have themes and messages, they can also follow the same (though more compact) structure as a full length novel and novels can be written in first-person perspective. Therefore A, B and D are incorrect. However, short stories are often too short to include subplots, which novels can accommodate.