______means that a program written for one computer system can be compiled and run on another system with little or no modification．

In ______, the only element that can be deleted or removed is the one that was inserted most recently.

Either you or one of your students ______ to attend the meeting that is due tomorrow.

Don’t ______ that rope, or you might fall.

Project ______is an uncertain event or condition that，if it occurs，has a positive or a negative effect on at least one project objective，such as time，cost，scope，or quality．

It seems that the writer _____.

 ______ twice a year, whether it is a car or a bus or a truck, is the rule that every driver must obey in this city.

It seemed to me that what she saw and heard _____ very interesting.

It seemed to me that what she saw and heard ______ very interesting.

______no air or water, there would be no life in the world.

According to the writer, it seems that _____.

At that time no one’s even studied the problem, _______ tried to do anything about it.