What can be observed only by observing its effects on gravity?

According to bowers, which of the following best describes the dominance of interest groups in the state of nevada over time? political machines dominated during the first 50 years; from 1908 to 1958 railroad and mining interests dominated; primarily gaming interests from 1958 to the present. the railroad and mining interests dominated during the first 50 years of statehood; political machines dominated from 1908 to 1958; primarily gaming interests have dominated from 1958 to present. gaming interests have always dominated. railroad and mining interests dominated from statehood until 1959; gaming interests have dominated from 1959 to present. no one interest has ever dominated at any one time.