--Mum, where is my toy car? You promised.
-- , my dear, but you know mum is pretty busy today. Tomorrow, OK?
A. So it is
B. So is it
C. So did I
D. So I did
网友回答
A. So it is
B. So is it
C. So did I
(答案→)D. So I did
解析：考查：so +主语+助动词，表示对上句话的肯定。根据“You promised.”你答应的。所以助动词应用did ，So I did 意为我是答应过。