An alpha particle enters a hollow tube of 4 m length with an initial speed of 1 km/s. It is accelerated in the tube and comes out of it with a speed of 9 km/s. The time for which it remains inside the tube is

• A.             \[8\times {{10}^{-3}}\]s      
• B.             \[80\times {{10}^{-3}}s\]
• C.             \[800\times {{10}^{-3}}s\]  
• D.             \[8\times {{10}^{-4}}s\]