Rough Endoplasmic Reticulum (RER) — Structure & Function

Which of the following best describes the ribosomes attached to the rough ER?

Image Sources:

• A: By Lorax GFDL or CC-BY-SA-3.0, via Wikimedia Commons
• B: Image source: By NAME CC0, via pixabay.com
• C: Image source: By Orlovic CC BY 2.0, via Wikimedia Commons
• D: Image source: CC0, via pxhere.com