You should ______ the wheels of your bicycle once a month.

A．The Southern colonies shared a common culture.
B．The Northern colonies shared a homogeneous culture.
C．Acquisitiveness was a characteristic unique to the South during the Colonial period.
D．There were significant differences between Puritan and Southern culture during the Colonial period.

A．anatomists and geneticists are morally questionable
B．genes are as much a part of a human form as pancreas
C．the pancreas has greater human importance than genes
D．people are more interested in patenting genes than pancreas

A．They are difficult to mark' off.
B．They contain unidentified genetic information.
C．They contain the entire human genetic information.
D．They are genes whose specific functions have been identified.