Carbon pollution from the burning of fossil fuels has contributed to

C should be the answer.
We can't determine the amount of carbon released simply from the fossil fuels.
Because fossil fuels are not the only source.
Carbons are getting released from the permafrost also.
So C is the answer.

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C could also be an answer as there is a clear mention: "that are now being spread into the atmosphere by bacteria as the permafrost melts."
Kindly help me with the answer

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Veritas Prep Official Explanation

With Inference questions, the correct answer must meet the "must be true" standard, which means that you should attack each answer choice via process-of-elimination. Also note that when you have prior knowledge of the subject matter of a question and/or when you have a strong opinion about a topic (as many do with topics such as the environment), you must take care to avoid "mental inertia" - you can only decide on an answer choice based on what is explicitly given in the stimulus.

With choice A, pay attention to the specific wording that the "rate at which carbon is being released" is increasing (NOT "the amount of carbon is increasing"). While it might seem likely that the addition of a new source of carbon would increase the rate, you cannot prove this from the information given (what if a combination of more fuel-efficient vehicles and fewer people driving has dramatically cut down auto emissions by more than the newly unfrozen carbon is being released?).

With choice B, you can use similar logic: you just don't know how much carbon is in the permafrost (at least not from the stimulus) and you cannot rule out a massive surge in the burning of fossil fuels. (Also note - predictions far into the future are really hard to prove. What if an asteroid blows the whole planet up next week? Even if the trend were heading in this direction, that would render the prediction untrue!)

Choice C is correct: the stimulus proves that now there is (at least) a second source of carbon emissions, so calculating the amount from just one of those sources will not give an accurate statistic.

Choice D doesn't have to be true (what if someone invents a "carbon vacuum" to clean the air?). And choice E is also incorrect - you know now that there are two sources of carbon, but do not have nearly enough information to declare that the two sources are equal in the amount of carbon they release.­