Question

英语：Tom went to the box office at lunch time， but all the tickets bad been sold out

Answer 1

Tom went to the box office at lunch time， but all the tickets had been sold out
过去完成时，简单理解成“过去的过去”
前面句子Tom went to the box office at lunch time，有went可知，是一般过去时，
汤姆在午餐的时间去了box office，但是所以的餐票都卖光了~~~
由句意可知，餐票是在汤姆(went)之前就卖光了，所以要用过去完成时，即：had done~~

又因票是卖光，所以要用那个被动语态~~
ticket作主语，要用被动，故had been sold out~