The image of a European dressed in their / his finery going out to gaze upon...
Should I use their or his?
In my opinion "their" is the correct pronoun because it refers to both men/women. Though, my SAT exam preparation book states "his" is correct because it refers back to a European, which is singular.
Why should I use "his" in the sentence above instead of "their"?
The image of a European dressed in his finery going out to gaze upon...
In this particular case, you're talking about just one European: "dressed" is referred to one of them - no matter what his/her sex is: it's just one person and you should use a singular possessive adjective. You should have used their if the noun to which "dressed" is referred had been "European people" or something similar.
I don't know exactly what you are trying to say with that sentence.
If you say "The image of a European in his finery" then I understand that you actually mean "The image of a male European"; similar for "her". When you use "their" the I understand that you mean "The image of a European, who could be either male or female...". So all three are correct, but with different meaning.
Using "his" for a single person who might be male or female seems confusing to me.
