I believe the answer would be c.
The correct verb would be "are".
Stefano is one of those few people who ARE very civic minded and actively involved in community affairs.
Why? Well, while we are in fact talking about Stefano, we are RELATING him towards the "few people". "Is" is a verb used for singular nouns while "are" is used more commonly among plural nouns.
solitude-isolation
jocund-happy
Isolation, while being the closest synonym to solitude, has a negative connotation. As if the writer didn't choose to be alone in bliss, but were rather trapped where they were- alone.
Happy is a commonly used word. It makes the writer/author seem elementary in their writing, which wouldn't fit in this poem as it's a high level poem that can be used for scholarly analysis.
Because he is
Cause I said so
Your welcome
