小题1:They performed Michael Jackson’s unfinished dance.
小题2:It is a group of people who meet in a public place to perform an activity for a short time.
小题3:Yes, they are.
小题4:On the Internet.
小题5:It is very surprised and strange.
小题1:细节理解题，根据文中语句“a lot of fans met at People’s Square in Shanghai. They performed Michael Jackson’s unfinished dance.”理解可知。
小题2:细节理解题，根据文中语句““Flash mob” is a group of people who meet in a public place to perform an activity for a short time.”理解可知。
小题3:细节理解题，根据文中语句“Sometimes all these people are friends, but usually they are strangers (陌生人) and they find each other (彼此) on the Internet.”理解可知。
小题4:细节理解题，根据文中语句“but usually they are strangers (陌生人) and they find each other (彼此) on the Internet.”理解可知。
小题5:细节理解题，根据文中语句““Flash mob” is very surprised and strange.”理解可知。