答案：B

本题考查句式结构和非谓语动词。句意：Mr. Smith看到他修好的车又坏了很失望。该题考查的是“have sth. done”结构。题干中的the car went wrong again为 see 后的宾语从句，he had had (the car) repaired 为 the car 所带的定语从句；定语从句谓语含have sth. done 结构，为过去完成时。因先行词car 在句中作 had 的宾语，故关系代词 that 或 which 被省掉。故答案为B.