PrepTest 117, Section 3, Question 24
By Brandon Beaver | Published October 29, 2024
Type: Must Be
Difficulty:
Explanations
This one’s a mouthful. Let’s consider what we know:
- In terms of mass: Stars > Brown dwarfs > planets
- If a star has mass equal to or greater than the sun, then it has lithium in its atmosphere because its furnace hasn’t consumed all of it yet
- If a star has less mass than the sun, then it has no lithium in its atmosphere because the furnace has fully consumed it
- Brown dwarfs don’t have similarly functioning furnaces, so they can’t consume their lithium
What can we infer from these facts?
According to the science journalist, these furnaces seem necessary for burning lithium. Since brown dwarfs don’t have these furnaces, then brown dwarfs must have enough lithium in their atmospheres that we can detect it. In other words, if you’re a brown dwarf, you’ve got at least some lithium in your atmosphere.
Let’s see.
A
Nope—confuses sufficient and necessary. This translates to, “If you’re a celestial object without lithium in your atmosphere, then you’re a star with less mass than the sun.” All we know is if you’re a star with less mass than the sun, then you have no lithium. There may be other lithium-free celestial objects than stars smaller than the sun.
B
Nah. This translates to, “If you’re a celestial object with lithium, then you have a nuclear furnace that isn’t done mixing elements.” We know this is true from the inference we made in our prediction. That is, brown dwarfs must have lithium in their atmospheres and they don’t have these furnaces.
C
Yes! Awkwardly worded, but no less correct. This translates to, “There isn’t a single brown dwarf without lithium in its atmosphere.” That’s almost exactly what we predicted.
D
No. This translates to, “If you have lithium in your atmosphere, then your mass is equal to or greaten than the sun.” Nonsense—brown dwarfs have lithium and are less massive than the sun.
E
No way. We learned nothing in the passage about celestial objects less massive than brown dwarfs.
Passage
Science journalist: Brown dwarfs are celestial objects with
Question 24
Which one of the following is most strongly supported by the