The drill in Antarctica dragged on slowly because of lack of money, equipment breakdowns, environmental_________ and severe cold.
We tried to _________his doubts and let him tell the truth.
The police ________him to see if he had a gun.
Is this museum _______some German friends visited the day before yesterday?
The visitors saw rows of houses the roofs _______are red.
As is known to all, China _______the group of developing countries.