This is false: it has a very negative connotation.
It refers to a smile that is mocking or contemptuous (or a remark that is mocking or contemptuos) - so it's not a genuine smile, but an ironic and sarcastic smile. It has a negative and not a neutral connotation.
He used to live in France as a boy .
There used to be trees in the garden. They used to come out in those days . I used to love her . How did you used to spend your winter evenings?
I would go with B. although because if you think and read. the sentence it make the most sense. hope this helps :)
