A researcher made an interesting observation about a protein made by the rough endoplasmic reticulum and eventually found in a cell's plasma membrane. The protein in the plasma membrane was actually slightly different from the protein made in the ER. The protein was probably altered in the __________.

• A. smooth endoplasmic reticulum
• B. plasma membrane
• C. transport vesicles
• D. rough endoplasmic reticulum
• E. Golgi apparatus