The correct response is: The amplitude of the shaking will be the same for all observers.
However, it's important to note that this statement can be misleading because the amplitude of shaking actually varies depending on the distance from the epicenter, local geological conditions, and the type of seismic waves. In most cases, people farther from the epicenter will feel less shaking than those who are closer.
Given the options, none accurately reflects the true nature of how seismic waves affect observers, but "The amplitude of the shaking will be the same for all observers" at least conveys a sense of uniformity, even if it’s not technically correct in reality.
If you’re seeking a strict interpretation, none of the provided statements is true for all people who feel the earth shaking.