The detail that Mateo should take out of his essay about unique animals is: "All mammals give birth to live young."
Mateo should take out the detail "All mammals give birth to live young."
The detail that Mateo should take out of his essay about unique animals is: "Elephants are the only animals that cannot jump." This detail is repeated twice in the list of responses, so it appears to be a duplicate. It is not necessary to include the same detail twice in the essay, so Mateo should choose one of the statements about elephants and remove the other.