If dimensions of critical velocity $v_c$ of a liquid flowing through a tube are expressed as $[η^x ρ^y r^z]$ , where $η, ρ$ and $r$ are the coefficient of viscosity of liquid, density of liquid and radius of the tube respectively, then the values of $x, y,$ and $z$ are given by :

Question

( A ) $ -1, -1, 1$
( B ) $-1, -1, -1$
( C ) $1, 1, 1$
( D ) $1, -1, -1$