This is true...What are you asking, exactly?
The answer is more anxious.
Answer: B
Explanation:
"icy" when describing a person's attitude or personality means cold, rude, etc, but a smile is usually happy and warm.
Personally I don't think it's an oxymoron- it's definitely possible to do a rude, fake smile. But B is what an oxymoron is- two words that are opposite in meaning and shouldn't technically be used together- like "awfully good" or "bittersweet."
Formal.
As far as I know, there is no such thing as either standard or practiced diction. Informal is the way you communicate with your friends, for instance, which is not how you would write a thesis paper, legal document, etc.