According to Newtonian mechanics, I. Mass is a quantitative measure of a body's inertia. II. Mass is a measure of the attraction of one body to another. III. Inertial and gravitational masses are equivalent. IV. Mass is invariant. Which combination is correct?

Inertia is one of the major symptoms of mass and is quantitative. According to Newton, an object remains stationary or moving unless  force is applied. Inertial mass and gravitational mass are the same. It is also correct that one mass attracts other masses by gravity according to the law of gravity. According to Newtonian mechanics, mass is invariant. It hasn't changed since Newton.