Shadows are made by blocking light. Light rays travel from a source in straight lines. If an opaque (solid) object gets in the way, it stops light rays from traveling through it. The size and shape of a shadow depend on the position and size of the light source compared to the object.
The answer to your question is "A. a lower frequency of the siren.
Because the person in back of the ambulance will hear a lower frequency of the siren. This is because the waves are stretched out. A longer wavelength results in a lower frequency.
