What __(happen) in the next room at this time last Sunday?

What __(happen) in the next room at this time last Sunday?
What __(happen) in the next room at this time last Sunday?

What __(happen) in the next room at this time last Sunday?
was happening
at this time 进行时态的标志 last Sunday过去时态的标志
所以这边用过去进行时态