PrepTest 152

The argument specifically states that the fish in the Amazon descended from the Pacific fish, so this answer is out of scope.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Hypothesis: The Amazon once flowed into the Pacific, even though it's not blocked off by the Andes and flows into the Atlantic.
Evidence: Freshwater fish that are descendants of extinct saltwater fish from the Pacific (and not Atlantic) live in the Amazon.

Answer Anticipation:
This argument discusses a wide variety of facts (mountains, fish of different types, oceans), so there are a lot of potential answers. Anything that connects the Pacific fish with the Amazonian fish, or rules out those fish coming from the Atlantic, will strengthen the hypothesis.

Answer Explanation:
These fish are the key evidence the author uses to support her conclusion. If the ancestor fish were around before the Andes formed, and the Andes are the blocker in the way of the Amazon going to the Pacific, then that increases the likelihood that, when those fish were still alive, they were able to swim into a non-Andes blocked, Pacific-flowing Amazon.

Key Takeaway:
When an argument throws a variety of facts your way, stay flexible when looking at the answers and consider anything that impacts any of the information from the argument.

Related to and descended from are different things. Additionally, the fish in question aren't known to be in the Atlantic Ocean at all.

Thanks for the geography lesson, LSAT! In any case, this provides context, but the extent of the Andes now doesn't increase the likelihood that, pre-Andes, the Amazon flowed in a different direction.

Since the fish in question already made the transition from salt to fresh water, this answer is out of scope.