A. vague: inattentive
B. faithful: resolute
C. malleable: tractable
D. concerned: obsessed
E. improvident: industrious

Firm evinces intransigent. So which pair expresses a relationship most similar to it, C. malleable: tractable or D. concerned: obsessed?

Thanks very much.
Gut reaction, Jeff... (followed by logic): D

Intransigence is an extreme condition of firmness.

Obsessiveness is an extreme version of concern.
Students: We have free audio pronunciation exercises.
Oh right. Thanks so much, Davkett. I didn't notice that.

So the second word expresses a concept stronger or more tense than the first one.
More intense, yes...though I prefer 'more extreme'.