What is the author's primary purpose in referring to the rate of growth of a North American lichen species (lines 29-...

shunhe on December 22, 2020

Hi @Melody,

Thanks for the question! We’re being asked here about the author’s primary purpose, or main reason, for referring to the rate of this lichen species in lines 29-30. So why does the author do that? Well, looking at those lines and the lines around them, there’s a greater discussion of timescales in general, and that’s what this is supposed to help you understand. It’s not (B), because the point isn’t just to offer an example of some lichen species that has one of the slowest known rates of growth. That can’t be the main purpose, when that’s not the focus of the passage. And in addition, the passage doesn’t say anything about this lichen species being an extra slow grower. It could be an average-growing lichen; nothing in the passage suggests otherwise, and that’s another reason you know it’s not (B).

Hope this helps! Feel free to ask any other questions that you might have.