1. At midnight, we (not hear) anything because we (sleep) .

2. As soon as we (received) a warning we (send) back a reply.

3. The frogmen (work) in the cave when they (make) the discovery.

4. John (take) the apple and (put) it in his mouth.

5. The car (explode) when it (crash) into a tree.

6. It (snow) when I (realize) that we had run out of fuel.

7. Mary (listen) to the radio when she (see) a stranger in the garden.