Answer is C because n^3/sqrt(n) is equivalent to n^3/n^0.5 which is equal to n^2.5 ,which is greater than prefer of n^2 .

All of the other option is less than order of n^2:

A : linear

B : n^1.98

D : linear

All of the other option is less than order of n^2:

A : linear

B : n^1.98

D : linear