Final answer:
In Greek mythology, Zeus placed Callisto in the night sky as a bear, which corresponds to the constellations Ursa Major and Ursa Minor; her son Arcturus is associated with the nearby constellation Bootes.
Step-by-step explanation:
The character Callisto from Greek legends was placed in the night sky by Zeus as a bear. This is reflected in the stars we see as the constellations Ursa Major and Ursa Minor, which translate to the Great and Lesser Bear. Callisto's son,
Arcturus, is not directly described as a keeper in the mythology but is represented by one of the brightest stars in the constellation of Bootes, which is near Ursa Major. Hence, the correct answer to the question 'Zeus placed Callisto in the night sky as one of these animals; her son Arcturus was her "keeper" in the stars' is a) Bear.