[Grammar] Began or Begun

[*pushkar*]

We were still standing in the queue when the film began or begun or had began or had began Please help me with a valid reason

 

[bhaisahab]

We were still standing in the queue when the film began or begun or had began or had began Please help me with a valid reason

We were still standing in the queue when the film began.

 

[*pushkar*]

We were still standing in the queue when the film began.

i also thought so but in my book, it is mentioned "Had begun". Please help

 

[bhaisahab]

i also thought so but in my book, it is mentioned "Had begun". Please help

Your book is wrong.