C. They get into a car accident
C. The best plans often come to nothing
The two words Bradbury uses repeatedly in this scene are "The beetle". The repetition adds to the suspense of the scene. Each time "the beetle" is repeated the reader can feel the car getting closer and closer. Because the sentences are very short and similarly structured, they speed up the pace of the scene just like the car is picking up speed.
The most likely answer would be C if the topic is toddlers.
HOWEVER if their is no information to support that it is about toddlers in your marital then it is most likely D.