at intervals
continuously
rarely
painstakingly
Answer is Right!
Answer is Wrong!
The correct answer is A. at intervals.
The phrase “on and off” means “occasionally or intermittently.” This is consistent with the fact that the man has been working on the research project for several years, but has not been working on it continuously.
The other options are incorrect because they do not accurately describe the man’s work habits.
- Option B, “continuously,” is incorrect because the man has not been working on the research project all the time.
- Option C, “rarely,” is incorrect because the man has been working on the research project for several years.
- Option D, “painstakingly,” is incorrect because there is no indication that the man has been working on the research project in a particularly careful or meticulous way.