单项选择题

People in a large area may possess the same DNA thread because ______.

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
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单项选择题
Which of the following CANNOT be inferred from the passage
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.
单项选择题
If two men suspected for some reason they have a common ancestor, ______.
A．we can decide according to their family tree
B．we can find the truth from their genetic markers
C．we can compare the differences in their Y chromosome
D．we can look for written records to prove their relationship
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