问题: Therewasonceatimewhenhumansgatheredwildplantstoeatinsteadof_____.
A: deliberatelygrowingvegetablesandfruits
B:appletreesareeasiertoplantthanotherfruittrees
C:theymustbeplantedonceayear
D:bothdecorativeandproductive
E:humansocietyprogressed
F:ameanstocurediseaseofvariouskinds
