So basically to strengthen this argument it was just to look for the line that hadn't played any role in supporting the conclusion? And then find the supporting evidence as the answer?

I was so confused in the video when he circled d because I was like how does that weakened the argument because D is just irrelevant.

Isn't there a simpler way to notice that B is wrong? Like it says that the population has to be over 250 to be self sustaining (so 251) but the stimulus just says "must reach at least 250" (so just 250 to be self sustaining)?

I'm still not seeing the use of lawgic, like I'm getting 80% or 100% on all of these practice questions by just using basic reasoning.