Without facts, we can't form a worthwhile opinion, for we need to have factual knowledge ______ our thinking.
We found the ruins ____.
Do you know ____Rome wasn’t built in a day means?
Huge trees on the green land were cut down, ____ the city being buried by sand.
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.