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: My mom had a 75 gallon fish tank. She had friendly freshwater fish in there. Every one of her birthdays, I bought her shark for her tank. I tried to turn her sweet tank into a shark tank. To my shagrin, all the shark died and were eaten by the sweet fish.
 selected sentence: My mom had a 75 gallon fish tank.

My mom buys a fish tank >Causes/Enables> My mom has a fish tank