Complex sentence: Such a frame of reference is shown by the red arrows in the figure, and is termed natural or intrinsic because the axes (s, n) continuously adjust the moving parcel, and so they are the most closely connected to the parcel's fate.
Split into simpler sentences: Such a frame of reference is shown by the red arrows in the figure. This frame is termed natural or intrinsic because the axes (s, n) continuously adjust the moving parcel, and so they are the most closely connected to the parcel's fate.