Carlos is the only one of those students who __________ lived up to the potential described in the yearbook.
I was told that "who" refers to "the only one" and ,thus, the verb should be "has lived..". Is that right?
Thank you very much
Only one has lived up to...
He has lived up to...
The phrase 'only one of those studends' is made up of a noun phrase and its object.
Object (prepositional phrase): of his students
The noun 'students' belongs to the preposition 'of'. That is, the true subject of the phrase 'only one of the students' is the noun 'one'. It's singular, 'who' refers back to it, so its verb must be singular too: who has lived up to.
All the best.