In these questions, the letters are linked in some way. Identify the relation and complete the last box. \[\text{B}\,\,\,\text{:}\,\,\,\,\text{Z}\] \[\text{E}\,\,\,\text{:}\,\,\,\,\text{C}\] \[\text{T}\,\,\,\text{:}\,\,\,\,\text{R}\] \[\text{O}\,\,\,\text{:}\,\,\,\,?\]

• A.  L            
• B.         K      
• C.  S            
• D.         M