You are presented with the quiz "Birch trees are wood that are used to produce what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "burning wood is used to produce heat" and "birch trees are deciduous and the wood burns hot and fast, as if soaked with oil or kerosene". 

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


 

     heat      