I posted this question before but it did not get much attention. Trying it again..I am not convinced with the OA.
Spectroscopic analysis has revelaed the existence of frozen nitrogen, methane and carbon monoxide on the surface of Pluto. Such ices have a tendency to vaporize, producing an atmosphere. Since the proportion of any gas in such an atmosphere depends directly on how readily the corresponding ice vaporizes, astronomers have concluded that the components of Pluto's atmosphere are nitrogen, carbon monoxide and methane, in order of decreasing abundance.
The astronomer's argument relies on which one of the following assumptions?
(A) There is no more frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane
(B) Until space probes reash Pluto, direct analysis of the atmosphere is impossible.
(C) There is no frozen substance on the surface of Pluto that vaporizes more readily than methane but less readily than carbon monoxide
(D) Nitrogen is found in the atmosphere of a planet only if nitrogen ice is found on the surface of that planet
(E) A mixture of nitrogen, carbon monoxide and methane is characteristic of the substances from which the Solar System formed.