Answer:
4th Option, share a common ancestor.
Explanation:
If two organisms have similar traits of DNA they probably share a common ancestor is the most suitable option to fill the blank.
When the two organisms have similar traits of DNA they probably share a common ancestor.
When the genes are shared so it preserved the ancestor record where they share with each other and excludes the bacteria.
And, if the DNA is the same for two organism so they would share the a common ancestor.
hence, the last option is correct.
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