GMAT Critical Reasoning (CR) | Re: Before 1986 physicists believed they could describe

Before 1986 physicists believed they could describe the universe in terms of four universal forces. Experiments then suggested, however, a fifth universal force of mutual repulsion between particles of matter. This fifth force would explain the occurrence in the experiments of a smaller measurement of the gravitational attraction between bodies than the established theory predicted.

Which one of the following, if true, most strengthens the argument that there is a fifth universal force?

A)