How do you find your missing pen—________

You’d better carry a(n) ________ tyre in theback of your car in case it breaks down on the way.

We are at a stage ________ it’s still too early to say whether the newly-elected president will bring hope to the US.

he was 12, Einstein had learned advanced mathematics by himself.

______ halfway through the exercise, the teacher changed his mind and collected all our papers.