Pluto Has an Atmosphere That Comes and Goes Over an Orbital

Pluto has an atmosphere that comes and goes over an orbital period, because

A) the atmosphere escapes into space because of the low escape velocity from Pluto.
B) the atmosphere is pulled away from the planet by interaction with its moon Charon.
C) the atmosphere "freezes out" when Pluto is at its farthest from the Sun.
D) chemical reactions between Pluto's atmosphere and gas expelled by its many volcanoes generate carbon dioxide, which is too heavy to stay aloft in the atmosphere.
E) it is replenished by comet impacts at the far point of its orbit, and dissipates at the near point due to heat from the Sun.