Fact 1: Ribosomes are sites where proteins are made.

Fact 2: Endoplasmic reticulum are membranes attached to ribosomes.

Given the two facts above, answer the question "What are membranes attached to sites where proteins are made?" with the following options: 
- the body's largest organ
 - Veins and arteries.
 - epidermis and dermis
 - layers of fat
 - cell walls
 - cell membranes
 - endoplasmic reticulum
 - brain cells


 

       endoplasmic reticulum  