The endoplasmic Reticulum is like an assembly line: The workers on the assembly line do their work, as the products move through the assembly line. Similar to the workers are the ribosomes on the reticulum, as they also do their work in a line. In the reticulum, like in a factory line, the proteins are produced, and like in the case of the facotry line, they are later sent to the other place in the factory or cell.
Answer: The correct answer is C. Vacuum.
Explanation: It was correct on my test : )
Species have similar characteristics, but they are rarely, if not never, identical; the difference between them is variation!
Hope this helps! :)