When( )you( )toLondon?(怎么做)

(will) (go)

when have you been to london
when have you gone to london
when did you go to london
都可以。。

when did you go to london ?
when will you go to london?
现在完成时很少与特殊疑问句连用

未来
do ...go
will...go
过去
have...been
have...gone
did...you