#24 - When volcanic lava solidifies, it becomes uniformly

[SGD2021]

Hello, I understood the question here to be telling us to focus on a specific conclusion ( "The argument that the direction of the Earth's magnetic field has changed over time requires the assumption that")-- the sub conclusion. So, I focused on the sub conclusion of the stimulus ("it must be that the direction...has changed over time") as opposed to the main conclusion, which is in the last sentence.

I was able to arrive at the correct answer doing so but was it correct to focus on the sub conclusion (meaning that, to answer this question, I focused on analyzing the link between the sub conclusion and its premises) or should I have focused on the main conclusion? (I would like to make sure I didn't misunderstand the question stem)

[Adam Tyson]

You did exactly what you were supposed to do, SGD2021! Nice job! Since the question is specifically about that sub-conclusion, that's what we need to focus on, and the assumption doesn't have to have anything to do with how long it takes for the direction to change (the main conclusion).