Mostly a good question. I got it wrong, because I was too hasty - I overlooked that the data type was DATE, not DATETIME (probably because I still work with SQL2005 on a daily basis). I do know that adding an integer to DATE is not supported.
What I dislike about the question is:
* The date format. Not all locale settings recognise "Dec" as december. (Try adding "SET LANGUAGE German;" as the first line - at least on SQL Server 2005 and with the data type changed to datetime, that results in a conversion error)
* The missing semicolons. In SQL Server 2008, not terminating statements with a semicolon is deprecated.
* There were two SELECT statements, so the incorrect answer options should have included two results sets. (I guess the author intended the first SELECT to read "SELECT @Today = @Today + 1;" - yet another reason to prefer SET over SELECT).
But the lesson learned is valuable. For me (to read carefully and think instead of just shooting from the hip), and for many others (that adding an integer to a date is not supported - just as it should never have been supported for datetime).
Thanks for the question!