Why have you had so many jobs in three years/for short periods of time?
Yes，you could say that,but as you can see,I always moved to positions with more reponsibilities and opportunities to acquire new skills.
I'm a quaick learner and an efficient worker.
I had accomplished as much as I could in each job and I felt it was time to move on for greater challenges and to make even greater contributions,whenever a new opportunity was presented.
After each move,my value as an employee grew.
Why did you change jobs so frequently?
You don't seem to be able to stay with one job for more than a year?