In these questions, the letters are linked in some way. Identify the relation and complete the last box. \[\text{10}\,\,\,\text{:}\,\,\,\,\text{30}\] \[\text{100}\,\,\,\text{:}\,\,\,\,\text{300}\] \[\text{1}\,\,\,\text{:}\,\,\,\,\text{?}\]

• A.  10                         
• B.         6            
• C.  3                            
• D.         5