Definition: In this task, you will be given a short story. One sentence from the story is chosen. Consider the events that happen before that sentence, or are likely to have happened before it. Does any of them directly cause it, or simply make it possible? You should write your answer in the form " A >causes/enables> B". Try to use phrases and sentences from the story to compose your answer when possible.
Input: story: Bob was sitting on the porch swing. The swing was very old. Bob had plans to fix it soon. Suddenly, the chain snapped and dropped bob to the floor. Luckily, ob's hard head broke his fall.
 selected sentence: Luckily, ob's hard head broke his fall.

Bob drops to the floor >Causes/Enables> Bob falls on his head