The Rough endoplasmic reticulum (ER) is a membranous organelle that found next to the nucleus and is covered in ribosomes.
The rough endoplasmic reticulum and ribosomes work together, ribosomes functions in the synthesis of proteins and rough ER helps in synthesis and transporting the proteins to their final destination. Hence, the rough ER's majorly functions in the formation and storage of proteins.
Thus the correct option is Rough endoplasmic reticulum.
