---_______ the farmers discovered the entrance to the secret cave in the valley?--- Totally by chance.
—Oh, dear. I forgot the air tickets. —You __________ something.
I think you two, __________ Tom, __________ the broken glass.
We should do more such exercise in the future, I think, __________ we did yesterday.
This photo of mine was taken __________ stood the famous twin-tower before the 9.11 event.
Though they met for the first time, they talked __________ they were good friends.