"How long have you been standing here?" he asked me. (HAD) ->......................................................................................................

`-` `A`nswer : He asked me how long I had been standing there.

`->` Câu gián tiếp `-` Wh-questions : 

`+` S + asked + sb + what/where.... + S + V(lùi thì) 

`->` Lùi thì : HTHTTD `->` QKHTTD (S had been Ving)

`-` Here `->` There 

`->` Anh ấy hỏi tôi đã đứng đó bao lâu rồi.