Read the excerpt from Sinbad the Sailor.

Question

During the voyage we touched at several islands, where we sold or exchanged our goods. We were one day becalmed near a small island. As its appearance was inviting, we determined to dine upon it. But while we were laughing and preparing for dinner, the island began to move, and at the same moment the people in the ship called out that we were on the back of a monstrous whale. Some jumped into the boat, and others swam to the ship; but before I could get off the animal dived into the sea, and I had only time to catch hold of a piece of wood that had been brought from the ship to serve as a table.

Which word helps readers determine when the island begins to move?

during
as
while
before