Logical reasoning PrepTest 120 · Section 1 · Question 12

Incorrect. While this answer does connect to the origins of human life, it doesn't connect with any of the three noted similarities, so this answer is incorrect.

Incorrect. This answer discusses "any living beings," not any "known" living thing. Additionally, it connects two of the similarities, not one of the similarities to the conclusion. While some arguments do require a connection between two premises to validate a conclusion, this argument's gap was between the premises and the conclusion.

Incorrect. The conclusion is about "known" life, not life that might crop up or be discovered in the future, so this answer is out of scope.

Incorrect. This answer doesn't connect to the origin of any living things, so it doesn't help justify the conclusion.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Sufficient Premise

Stimulus Summary:
All known living things:
(1) Made up of the same basic matter
(2) Carbon-based
(3) Genetic codes
So all life has the same origin

Answer Anticipation:
The argument here brings up three similarities between all known living things, and then concludes that all known life (humans included) has the same origin.

The origin of these various forms of known life is completely unmentioned in the premises, so that's a new concept in the conclusion that we'll need to connect to one of the premises in order to allow the conclusion to follow logically.

In a question like this, it's easy to anticipate that all of the three similarities will show up in the correct answer. However, any of the three similarities individually could justify the conclusion, as could any combination of them. Therefore, we should look for an answer that states any of the three similarities alone or together means that the lifeforms have the same origin.

Answer Explanation:
The argument establishes that one similarity between all known living things is that they are made of the same basic kinds of matter. If, as this answer choice states, that means they have the same origin, then the conclusion is valid. This is the correct answer.

Key Takeaway:
While many Strengthen with Sufficient Premise questions use all of the premises in the "complete" argument, others will introduce extraneous information, or they'll present information that could be relevant with one potential correct answer, but not with the actual correct answer provided. Don't feel the need to connect all the premises to the conclusion—an answer that connects any premise to the conclusion will generally serve to allow it to follow logically.