When an incoming wave combines with a reflected wave in such a way that the combined wave appears to be standing still, the result is a
a. longitudinal wave.
b. standing wave.
c. transverse wave.
d. surface wave.

A sound wave is a pressure wave that results from the vibration of the particles o the medium from the source. The motion of the particles in the medium is parallel to the direction of the energy transport. The type of wave formed by a sound wave is the longitudinal wave. The answer is letter C. A longitudinal wave is characterized by rarefactions. When motion is detected from the source, the particle next to it vibrates from its rest position and a progressive change in phase vibration is observed at each particle within that wave. The result is that the energy is transported from one region to the other.

that would be b i just took the test : )

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue