* Ursus arctos is the scientific name for the brown bear.

* Ursus maritimus is the scientific name for the polar bear.

Both brown bears and polar bears belong to the same genus, Ursus. This means they are more closely related than the other options.

Let's look at the other options:

* Felis ursus - This name doesn't exist. "Felis" is the genus for cats, and "ursus" is the genus for bears.

* Felis felis - This is the scientific name for the domestic cat.

* Ursus Felis felis - This is a combination of the genus for bears and the scientific name for cats, and therefore not a valid scientific name.

Key takeaway: Organisms with the same genus are more closely related than organisms in different genera.