PT152 S4 Q12 ExplanationThe Amazon River flows eastward

Answer choices, explained

1. A

   No Impact / Weak2% picked this

   In many cases, species of freshwater and saltwater fish that share certain characteristics do not in fact

   I'm happy that's the case, in many cases. Unfortunately, it's not the case in this case. Here, we're talking about a freshwater species that has a saltwater ancestor. So this answer isn't relevant to the conversation. (It's also very weakly worded and it sounds like it has the tone of pointing out an objection)

   2%
2. B

   Correct84% picked this

   Most of the fossilized remains of the now-extinct saltwater fish from the Pacific Ocean date to a period prior to the

   Why this is right

   This is suggesting that when this Pacific saltwater ancestor lived, the Andes Mountains had not yet formed. That increases the plausibility of the author's causal story -- she thinks that the freshwater fish in the Amazon whose ancestor is this Pacific saltwater fish got where it is because at some point the Pacific Ocean and the Amazon river were connected. In order for this storyline to work, it needs to be true that when the saltwater fish was alive, there was some connection between the Pacific and the Amazon. Since those two things are currently disconnected by the Andes Mountains, if the Andes Mountains didn't exist yet, then the two bodies of water could commingle.

   Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.

   84%
3. C

   Irrelevant Distinction / Weak10% picked this

   Many species of fish that inhabit the Atlantic Ocean are related to fish species that are known to

   Our conversation has a fish that inhabits the Amazon River, related to a fish that only inhabits the Pacific ocean, and that's a bit of a Curious Fact, since the Amazon and the Pacific are currently cut off from one another. This weak idea that "at least 5-10 species of fish in the Atlantic Ocean are related to something in the Pacific" has no impact on that conversation. The Atlantic and Pacific Ocean are not cut off from one another.

   10%
4. D

   No Impact2% picked this

   The Andes Mountains extend from the northernmost to the southernmost extremes of the

   This is just fleshing out what the concept of "cut off from the Pacific Ocean" means. Whether the mountains cut off the Amazon river by a straight vertical line or a diagonal line, or an L-shape, doesn't matter. They're currently cut off. This answer is focused on the present, whereas our hypothesis should have us wanting to get more information about the past.

   2%
5. E

   No Impact2% picked this

   There are very few fish species that are known to be able to survive in both

   This the third answer choice now that is just saying some generality about fish in the world. We need some specific information about the Amazonian freshwater fish that are descended from the Pacific-only saltwater fish, or more information about the Amazon River / Andes Mountains / Pacific Ocean.

   2%