You are presented with the quiz "What are membranes attached to sites where proteins are made?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "ribosomes are sites where proteins are made" and "endoplasmic reticulum are membranes attached to ribosomes". 

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


 

       endoplasmic reticulum    