Nice attempt at the question, however I think this one is flawed

Seeing how result two does not need the parentheses that is

SELECT @a + (@B-@C) AS 'Result #2'

is the same as

SELECT @a + @B-@C AS 'Result #2'

And there is only one answer with 1 as the second option. The user can guess at the answer without understanding the concept

I would have thought

SELECT @a + @b-2 * @C AS 'Result #4'

would have been more challenging without the parentheses for most people.