So I was还是So I did

--It was careless of you to have left your clothes outside all night.

--My God! ____.

A. So did I     

B. So I did     

C. So were you 

D. So did you

请问这题的正确回答为何不是So I was. 而是So I did呢？

回答= My God!  I did leave my clothes outside all night. 所以用 So I did. 我确实忘了收衣服了。