Tom, clean up the broken glass _________ someone walks on it.
When it______ air pollution, Beijing faces the three “C” s-----cars,coal and construction,which lead to Beijing's thick air pollution.
______ it have been the failure to pick up directions from the ground control that caused the air crash?
The one concern for parents and students is ______ if the student pursues their university education in a foreign country, the student will not have the opportunity to establish social contacts in China.
Not until the train pulled into the next station ______ her suitcase gone.
In class, fewer of the students who are not ___ their studies sometimes ____the dying robots, not listening attentively.