he asked me when did i graduate为什么是错误的?应该填he asked me when i graduate不是要改成陈述吗

he asked me when did i graduate
为什么是错误的?应该填he asked me when i graduate
不是要改成陈述吗

when 引导宾语从句,应该用陈述句语序.when did i graduate是疑问句语序,是错误的.
改为：He asked me when i graduated.宾语从句的时态语主句保持一致,用过去式.