To find out the answer of this lets solve each answer first and then we will see which is the smallest. Lets do:-
A) √401 = 20.02498439
B) ∛8000 = 20
C) 5² = 5 × 5 = 25
D) 3³ = 3 × 3 × 3 = 27
So the smallest of these numbers is B) the cube root of 8000.
Hope i helped ya!!