All of us did quite a good job but the teacher only ______ him out for praise.

A．We are a walking, living, breathing record of our ancestors.
B．Many American slaves did not know who their ancestors were.
C．An adopted child generally lacks enough information to prove his identity.
D．Molecular genealogy can be used to prove a relationship between individuals.

A．DNA is characteristic of a region
B．they are beyond doubt of common ancestry
C．DNA strand has the ability to identify individuals
D．their unique identification can be provided via DNA