The correct answer is theory of general relativity.
Explanation:
According to the statement of equivalence the gravitational mass force on an object standing on the surface of earth is same as the pseudo force that acts on it if it accelerated at acceleration equal to acceleration due to gravity.
According to Einestine both the forces are indistinguishable as both the forces produce same effects. Thus both are equivalent and thus gravity is a phenomenon that can be analysed in a radically different way which gives some strange results such as bending of light, existence of black holes,e.t.c
