Reducing speed limits neither saves lives nor protects the environment. This is because the more slowly a car is driv...

shunhe on July 20, 2020

Hi @Anna2020,

Thanks for the question! Let’s take a look at the stimulus here. We start off with the conclusion: reducing speed limits neither saves lives nor protects the environment. Why do we know this? Well, the more slowly you drive a car, the more time it spends on the road while it’s spewing exhaust, which also makes it a longer time that it could crash into another car.

So now we’re asked for a flaw in this reasoning. And one should come to mind straight away: this argument is super focused on time, and says that the longer you’re on the road the more emissions and the more likely you’ll crash. But what if driving slower reduces the probability that you crash at any given moment? And driving slower reduces your emissions per given time interval? The answer will likely have something to do with this.

Now look at (D), which tells us that the argument presumes without justification that the total emissions for a given automobile trip are determined primarily by the amount of time the trip takes. Well, that is exactly what the argument does. By ignoring other factors like efficiency at different speeds, that’s what the argument does, which is a flaw as discussed above. That makes (D) the right answer.

Now take a look at (E), which tells us that the argument presumes without justification that drivers run a significant chance of collision only if they spend a lot of time on the road. First of all, we aren’t told anything about how “significant” the risk of collision is for anyone, which suggests that this answer choice is going too far in its wording. Also, the argument definitely doesn’t presume that there’s a significant risk of collision ONLY IF drivers spend a lot of time on the road. The argument could assume that there’s a significant risk of collision in other cases where the driver doesn’t spend a lot of time on the road (like if they’re driving blindfolded) and still be fine, so this isn’t something the argument assumes. Those are both reasons (E) is wrong.

Hope this helps! Feel free to ask any other questions that you might have.