Answer Choice A

I think the first answer I would have to this is that A simply doesn't pass the 'so what' test. I struggle to see how or why it is relevant to the argument. For strengthen and weaken questions, if there is no "so what" to an answer choice, it's quite likely it doesn't strengthen or weaken that argument. More specifically, we should look at what the argument is actually about. This argument is that the amount of pollution that US cars will contribute to global pollution will fall. This is true regardless of whether air currents circle the globe. The argument is about the contribution of US cars to global pollution, and that contribution would be the same regardless of if all the pollution stays in US airspace or if it travels.

You're right. Thank you Emil