In these questions, the letters are linked in some way. Identify the relation and complete the last box. \[\text{3}\,\,\,\text{:}\,\,\,\,\text{30}\] \[\text{9}\,\,\,\text{:}\,\,\,\,\text{90}\] \[\text{1}\,\,\,\text{:}\,\,\,\,\text{?}\]

• A.  100                       
• B.         01         
• C.  10                         
• D.         001