The author of "Auld Lang Sync" Robert Burns was a great ______folk poet.

A．aerobic exercise help prevent lung diseases
B．vigorous exercise is dangerous for poeple over 50
C．weight lifting can do much good to the frail elderly
D．the more exercise one does, the less one is likely to die

A．a greater concentration of middle-class residents in central cities
B．a sharp decline of the life quality in central cities
C．a boom in setting up factories and offices in central cities
D．a rapid development of public transportation