You are presented with the quiz "Lack of what in the blood can lead to impotence? " 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "endocrine hormones travel throughout the body in the blood" and "deficiencies in the Endocrine System are another source of impotence". 

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


 

 hormones          