- Many jurisdictions require cars to pass emissions
+
This has caused cars that fail inspection to get off the road while owners buy newer cars
→
The burden of pollution of older U.S. cars will be gradually reduced over the next decade
This argument is assuming that the older vehicles, while taken off the road in jurisdictions with such emissions standards, are NOT going elsewhere. The stimulus only said that "many" jurisdictions are requiring these emissions tests - this doesn't tell us much! Perhaps "many" is only 5% of the U.S. while this argument is talking about the entire "burden of pollution" of older U.S. vehicles. With that said, it is important to note that we actually don't care too much about the newer vehicles. Why? Because the conclusion is strictly talking about "older United States automobiles." Therefore, knowing that "newer U.S. automobiles are terrible for the environment and will result in our demise" would actually do us no good for the purposes of this argument.
- (A) So? Does this say anything about older U.S. cars? Nope.
(B) This actually might strengthen the argument, if anything, by showing that newer cars will be better for the environment always. However, this still doesn't say anything about older cars and that is what we need.
(C) Yes! If there is a "thriving market" of people waiting to buy these older U.S. cars then we can safely question that the burden of pollution will be reduced. If anything, the burden of pollution would stay roughly the same BECAUSE do not actually seem to be ceasing existence. They are still going to be driven! Thus, the pollution in the global atmosphere should be about the same as it was before.
(D) Tricky! However, this doesn't really do too much. This seems to say that the number of jurisdictions are staying the same. Without making any additional assumptions, this seems to neither strengthen nor weaken the argument. If the same jurisdictions are going to be requiring the test - and no more - then why would we question the conclusion that the older U.S. automobiles will be contributing less pollution to the globe? It seems fairly reasonable. HOWEVER, if this answer choice had actually said that the number of jurisdictions were "sharply decreasing" then you might be onto something here...
(E) This might weaken but the problem is that we would have to make another assumption to make this so. We would have to assume that the "total number of automobiles in use" actually do "increase significantly." This is something we know nothing about so I would be hesitant to pick this answer! We have no idea how many cars will be on the road.