A rocket stays initially at rest. After ignition, rocket has a constant upward acceleration of 90 m/s², and reaches a final velocity of 5400 m/s. How long does the rocket take to reach to this final velocity?  $\textasciitilde$  $\textasciitilde$  $\textasciitilde$ 
选项为:A:$$1s$$  B:$$2.25s$$  C:$$60s$$  D:$$120s$$  请回答其中一个选项.