For similarity, in addition to models being geometrically similar to prototype, the following in both cases should also be equal____________________?

A. ratio of inertial force to force due to viscosity
B. ratio of inertial force to force due to gravitation
C. ratio of inertial force to force due to surface tension
D. all the four ratios of inertial force to force due to viscosity, gravitation, sur-face tension, and elasticity