@odevitt so the conclusion here is, "life on Earth may have started when living microbes were carried here from Mars on a meteorite."
The support?
Premise 1: Earth was bombarded repeatedly by comets and asteroids early in its history. This bombardment probably sterilized the surface and prevented life from originating during this early period in Earth's geological history.
Premise 2: Meanwhile, Mars escaped severe bombardment, and
Subsidiary Conclusion: So there could have been microbial life on Mars prior to there being such life on Earth.
Premise 3: Because many meteorites originating from Mars have landed on Earth
The question here is asking us to identify the role played by "there could have been microbial life on Mars prior to there being such life on Earth."
"So" is a structural indicator of a conclusion so this is clearly a subsidiary conclusion of the argument. Notice that this statement is supported by Premise 1 and Premise 2.
Additionally, the statement that "there could have been microbial life on Mars prior to there being such life on Earth" is required for the argument's conclusion.
You can see this by negating this statement, i.e. there could NOT have been microbial life on Mars prior to there being such life on Earth.
This would destroy the argument's conclusion that "life on Earth may have started when living microbes were carried here from Mars on a meteorite," so this statement is also required in order to establish the argument's conclusion.
This is why (C) is the correct answer.
You can eliminate (A) and (B) just based on "a claim for which no justification is provided."
(D) is eliminated because even if true, this statement does not guarantee the conclusion, i.e. it is still possible life on Earth originated on Earth.
(E) is eliminated because the statement is required in order to establish the conclusion.
Hope this helps! Please let us know if you have any other questions.
