We ...(work)when we ...(hear)something strange.
were working/heard
What...(you/do)when the postman ...(arrive)?
were you doing/arrived
It ...(rain)when I ...(come)out of the building.
was raining/came
We...(have)dinner when the phone...(ring).
were having/rang
We...(not have)dinner when Grandad ...(call)
weren't having/called
Marty...(not brush) his teeth when the lights ...(go)out
wasn't brushing/went
Julie...(walk) to school when she...(see) the accident.
was walking/saw
I...(cycle)to school when it...(start) to rain.
was cycling/started
The children...(study) when their mum...(ask) them to help her.
were studying/asked
Frank and Beth ...(sit) on the sofa when their parents...(come)home
were sitting/came