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 of common ancestry
C．DNA has the ability to identify individuals
D．their unique identification can be provided via DNA
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单项选择题
The possible research of family trees is based on the fact that ______ .
A．genetics has achieved a breakthrough
B．genetic information contained in DNA can be revealed now
C．each individual carries a unique record of who ho is and how he is related to others
D．we can use DNA to prove how distant an individual is to a family, a group or a population
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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