Hi, let's take a look at the argument. The author tells us that landfills have a lifespan of about a decade. This information seems like context, or a premise, it is just a fact.
The author then claims that some people think that as landfills become full, there will become a crisis of availability in the near future.
Finally, the author disagrees with this view. They reason that the people who think there will be a crisis ignore the fact that new landfills will be built, which would thus avoid the crisis.
We are then asked what role in the argument the claim that a crisis will occur plays. Since we know the author is rebutting that claim, we should expect the correct answer to be in that direction. This is a good match for D.