"He has a cat."
Translation:Él tiene un gato.
"una gata" should actually be accepted, because "una gata" refers to a specifically female cat. It's not uncommon in Spanish to change the ending of a noun that's normally masc. or fem. to match with the actual gender of the object, if the object is alive.
Please report this if it is not currently accepted, as it's a valid phrase in Spanish.