Signals sent from the human brain through the phrenic nerves induce synchronous spasms of the diaphragm. These spasms are commonly known as hiccups. The mechanism of hiccupping in humans is remarkably similar to the inhalation of water into the gills of many amphibians, as part of their method for exchanging gases when in aquatic environments. Which statement is true regarding hiccupping in humans?

a. Hiccupping in humans is a residual effect of the amphibian stage of embryonic development.

b. Hiccupping is a vestigial reflex that suggests a common ancestry between humans and amphibians.

c. As in the amphibian, human hiccupping is a method through which organisms efficiently exchange gases with their environment.

d. The presence of hiccupping in humans indicates that humans once inhabited aqueous environments.

Hiccupping refers to an involuntary contraction of the diaphragm that usually occurs several times per minute. Some research has suggested that hiccuping is an evolutionary remnant of amphibian respiration. This is because the mechanism is remarkably similar to the way tadpoles gulp air and water across their gills. This would mean that hiccups exist due to an antecedent to modern lung respiration.