In the first second of its flight, a rocket ejects 1 /40 of its mass with a velocity of \[1200\text{ }m\text{ }{{s}^{-1}}\]. The acceleration of the rocket is

• A. \[20\text{ }m\text{ }{{s}^{-2}}\]                
• B.        \[30\text{ }m\text{ }{{s}^{-2}}\]    
• C.        \[40\text{ }m\text{ }{{s}^{-2}}\]                
• D.        \[60\text{ }m\text{ }{{s}^{-2}}\]