Answer:
well
Step-by-step explanation:
The complete question is
The budget report for last year was very _____ researched.
- well
- much
- good
- complete
The word 'well' is the best option of this question. It is used as an adverb, which implies that the report was done in a good or satisfactory manner. It can be used as a synonym for skillfully, effectively, expertly, professionally, excellently, etc.