Interesting question.

I managed to get it wrong by forgetting that += was introduced in 2008, not 2005.

One comment though: depending on settings of ARITHABORT and ANSI WARNINGS, it is quite possible that none of the answer options will result, because the batch is terminated before it reaches the select statement. I expect some people will say "just assume the defaults", but the defaults are quite different for batches run from an SSMS Query Window and for batches run from user applications (ANSI WARNINGS is ON by default in the former case, and OFF by default in the latter case) so perhaps questions like this ought to specify the settings.