Not necessary, because even if the Hydro is not the “most” popular highly fuel-efficient car available, we still know that its sales are rising, and we still can attempt to explain those increasing sales by citing to the desire of people to appear environmentaly conscious.

Necessary, because if this were not true — if the Hydro is NOT recognizable as environmentally friendly in a way that its competitors are not (in other words, if people perceive the Hydro and its competitors are similarly friendly to the environment) — then the author’s explanation doesn’t make sense. The desire of people to appear environmentally conscious wouldn’t explain the Hydro’s sales, because that same desire should also be expected to cause people to buy the competitors, too; however, the sales of other fuel-efficient cars are declining.

Not necessary, because the argument’s reasoning has nothing to do with the Hydro’s safety record.

Not necessary, because even if Hydro buyers are NOT more likely to have neighbors who also drive Hydros, those buyers can still be motivated in their purchase by the desire to appear environmentally conscious to those neighbors.

Not necessary, because even if Hydro buyers have equal or more interest in environmental causes compared to buyers of other fuel-efficient cars, Hydro buyers can still be motivated in their purchase by the desire to appear environmentally conscious to those neighbors.