Select the option that is related to the fourth term in the same way as the first term is related to the second term and the fifth

Select the option that is related to the fourth term in the same way as the first term is related to the second term and the fifth term is related to the sixth term.

729 : 90 :: ? : 56 :: 512 : 72

A.            323

B.            343

C.            352

D.            335

Sol:

Pattern follows here is:

If (a : b) then b = x(x+1), a=x³

The required number is:

56 = ,7*8, ? = 7³