We know the outer core of the Earth is liquid because some earthquake waves are absorbed in the outer core. This is best represented by option D.
The behavior of seismic waves notifies us of the outer core’s shape in that shear waves (or S-waves) cannot travel through liquid, while primary waves (P-waves) can propagate through both solids and liquids. A seismic study cited that shear waves weren’t detected in particular parts of Earth, specifically the outer core. This is called the S-wave shadow zone phenomenon, and because s-waves were noted to have not been able to travel through liquids, we hypothesize the outer core of Earth is liquid.