Critical Reasoning

Spectroscopic analysis has revealed 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 astronomers' 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 reach 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.

OA is C.
I agree with the OA. However, I have a doubt with choice A. If we use the negation technique, and we assume that "there is MORE frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane". The conclusion could be weakened. Let me explain:

The argument says that the the RATE OF EVAPORIZATION of each ice (readiness) determines the proportion of each gas in the atmosphere. However, let's suppose that Nitrongen (the most abundant in atmosphere) has the lowest rate of evaporation but it is the most abundant as ice on the surface ( my negation technique). Nitrogen would be the most abundant in atmosphere not by the rate of evaporization, but by the amount of nitrogen on the surphace. The reasoning of the author would be weakened

Thanks!