She <span>had been working</span> on the project for 2 days before she finished it. So B is the only right one as it's a continuous action before an action with an exact defining past perfect continuous. Also there's a key word "for" that can help us to find out the tense.
The answer is C Specific feedback that focuses on the positive aspects of the essay
C - Beautiful antique instruments renames guitars
Appositives are nouns or noun phrases that renames another noun beside it. The phrase 'beautiful antique instruments' renames and is right beside 'guitars' as it is describing them.
Is there a second part to the question? Or is there a picture to go with it?