You are presented with the quiz "When the rain stops the stem used for storing water is fat because the what drink the water" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "acactus stem is used for storing water" and "when the rain stops the cactus is fat because the cactus roots drink the water". 

So, what's the best answer to the question?


 

        roots   