Answer:
The firefly has a smaller mass
Step-by-step explanation:
From Newton's law of motion, the reaction force on both the bus and the firefly are the same. Recall that Newton's third law states that action and reaction are equal and opposite.
Since the mass of the firefly is far smaller than the mass of the bus, the firefly splatters against the windshield since it is less able to withstand the high acceleration that results from the interaction of the two bodies.