QUOTED SPAM REDACTED - SS
Fortunately, my bother has not written his data on this USB flash drive.
And after reading your answer, I have followed your steps and download these two mentioned data recovery freeware. Both of them work well. The first one finishes the scanning process in seconds and finally restores the most part of my data. As to the second one, even though it takes nearly twenty minutes to scan the drive, it finally retrieves all my deleted files back. It is really free and efficient.
Thank you very much!!!!!