Although Pluto has an atmosphere and is much larger than any asteroid, Pluto is not a true planet. Pluto formed in or...

Letitia on December 19, 2018

Prep 66, section 4, Q17

Can someone please explain? I got B as my answer.


Ravi on December 19, 2018


Happy to help. This is a strengthen with a sufficient premise question. The conclusion of the argument is that Pluto is not a true planet. We know that Pluto has an atmosphere and is much larger than any asteroid.

The author supports her conclusion by stating that Pluto formed in orbit around the planet Neptune and was then ejected from orbit around Neptune when Triton, Neptune's largest moon, was captured by Neptune's gravity.

We have

P: formed in orbit around Neptune

C: Pluto not a planet

In order to make this a valid argument, we need to connect the premise to the conclusion so that we have P - >C.

Answer choice (A) tells us if something is a moon, then it is not a planet. However, we do not know whether Pluto is a moon, so we can eliminate this answer. If the stimulus had established that Pluto was a moon, then this answer would have worked as a sufficient premise.

Answer choice (B) does nothing for us. We know Pluto has an atmosphere, but this tells us nothing about whether or not it is a planet.

Answer choice (C) fails to give us a bridge from the premise to the conclusion. This answer would not 100% guarantee the conclusion of the argument.

Answer choice (D) does nothing for us. Nowhere in the stimulus is there any mention of size, so we can get rid of this answer.

Answer choice (E) is exactly what we're looking for. It maps to Planet - ->formed around the sun, which is the contrapositive of the structure of the argument in the stimulus (/C - ->/P). This is the equivalent of P - >C, so we have a sufficient premise that will make our argument valid.

Does this help? Let us know if you have more questions!