----Why did you cancel your trip to the New York? ----We were just about to leave ________ it started to snow.
Loulan is believed ____ by sandstorms from AD 200 to AD 400.
In 89 BC, Pompeii became a rich and busy city and near the city ____ a volcano.
While the soldier’s idea was interesting, the system was too difficult to be ____.
In old days, books for blind people used paper ____ against metal wire to form letters.
One winter day ____, he saw the tracks of animals in the snow and observed that the appearance of each one was different.