This question was a simple one and could be dealt simply by using common sense.
The social cost of carbon (SCC) is a monetary estimate of the economic damages that would result from emitting one additional ton of greenhouse gases into the atmosphere. The SCC puts the effects of climate change into economic terms to help policymakers understand the economic impacts of decisions that would increase or decrease emissions.
Of the options given, clearly option A makes sense and is the correct one. Options B, C and D are random statements and hence can easily be eliminated.