A force is represented by $$F = ax^2 + bt^{1/2}$$, where $$x$$ = distance and $$t$$ = time. The dimensions of $$\frac{b^2}{a}$$ are :

A

$$[ML^3T^{-3}]$$

B

$$[MLT^{-2}]$$

C

$$[ML^{-1}T^{-1}]$$

D

$$[ML^2T^{-3}]$$