Thanks for the question! So let’s walk through this stimulus first, since we can’t complete the argument without understanding the argument.
We’re told that having too much CO2 is bad and can only be stopped if we stop burning fossil fuels. But a country that does this will hurt its GNP. No nation would do this by itself. And so, the argument concludes, we won’t avoid the consequences of too much CO2, unless…?? And now it’s up to us to put something in that “unless.” This is a question where we can kind of try to think up the answer in our head and see if any of the answer choices match it. So it talks about how countries won’t do it by themselves. But what if countries do it together? That sounds like it makes sense. Countries won’t act themselves. So unless they act together, we’ll face the consequences. And (C) sums this up perfectly, it tells us that we’ll face the consequences unless international agreements produce industrial emission standards. So if we have international agreements, then everyone’s working together, and no one is bearing singlehandedly the costs.
Hope this helps! Feel free to ask any other questions that you might have.