Answer: B. a five-minute walk around the block
Explanation:
In the context of the text provided, the term "brief" refers to something having a short duration, or not lasting for long.
The text claims that, compared to scalp hair, "eyelashes have a very brief growth phase" because the growth phase of eyelashes is 30 days, whereas head hair has the longest growth phase: between two and seven years.
Compared to a twelve-hour flight across the ocean and a two-hour nap on the couch, a five-minute walk around the block is the briefest activity.
