As used in line 30, “sober” most nearly means

Answer 1

Without seeing the other words in the line, nobody can really answer. It could mean serious, subdued, calm, or not affected by alcohol. Sober has more than one meaning, and we don't know how it's used in the context. I would replace the answer choices with sober and see if one word clearly works better in the line/sentence than the other words/answer choices.