Here's a problem to solve: Proteins that are synthesized in ribosomal subunits undergo extensive post-translational modification and are packaged and directed to the appropriate destination. Which structural component of a cell is involved in such modification?

Among the 4 following options, which is the correct answer?

- A: endoplasmic reticulum
 
- B: lysosomes
 
- C: mitochondria
 
- D: Golgi apparatus
 