The petrol tank of an automobile can hold f, litres. If a litres was removed when the tank was full, what part of the full tank was removed?

• A. \[\ell -a\]                      
• B.  \[\frac{\ell }{a}\]
• C. \[\frac{a}{\ell }\]                                
• D.  \[\frac{\ell -a}{a}\]