Membranes of the endoplasmic reticulum (ER) may bear ribosomes when the ER is called Granular or Rough Endoplasmic Reticulum. It is abundant in cells engaged in active secretion. The attachment between ribosomes and endoplasmic reticulum is through signal recognition particle or SRP linked to 60S subunit of ribosome and ribophorin present over the ER. Thus, the correct answer is option A.