when did it happen和 when has it happend?有什么区别

when did it happen和 when has it happend?有什么区别 Could you tell me when did it happen why did it have to happen.why did it all have to end.when i When did it start? my farther asked me_____.A.when did it happen B.where it hap 是when did it started还是when did it start? ----How did it happen? ----We ____ on the lake when suddenly when did it start? 解释 when did you have it When did you know it? when 与 what time is it 有什么区别? when were you stading和when did you start有什么区别吗?