Answer: D.
D is rough endoplasmic reticulum present in the cell. This structure is responsible for production, processing and transportation of protein within the cell. The endoplasmic reticulum is the organelle which remains attached with nuclear envelop. The rough endoplasmic reticulum is studded with ribosome. The ribosome causes specific RNA molecules to pass through the endoplasmic reticulum and results in protein synthesis. The proteins being synthesized are transferred from endoplasmic reticulum to other parts of cell or out of the cell.