You are presented with the quiz "Endoplasmic reticulum are what attached to structures in the cytoplasm 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 structures in the cytoplasm where proteins are made" and "endoplasmic reticulum are membranes attached to ribosomes". 

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


 

   membranes        