Critical Reasoning (CR) | After a hepadnavirus inserts itself into a chromosome

After a hepadnavirus inserts itself into a chromosome of an animal, fragments of the virus are passed on to all of that animal's descendants. A hepadnavirus fragment is present in a chromosome of the zebra finch and in precisely the same location in a corresponding chromosome of the dark-eyed junco. The fact that these two bird species diverged from each other about 25 million years ago therefore means that the hepadnavirus is at least 25 million years old.

Which one of the following, if true,
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