Power number is the ratio of
(A) Drag stress to inertial stress
(B) Inertial stress to drag stress
(C) Inertial stress to gravitational stress
(D) Gravitational stress to drag stress
(A) Drag stress to inertial stress
(B) Inertial stress to drag stress
(C) Inertial stress to gravitational stress
(D) Gravitational stress to drag stress