The rain was heavy and _________ the land was flooded.

.．As is often pointed out, knowledge is a two-edged weapon which can be used_____________for good or evil.

 With more and more farmers moving to cities, an inadequate labor force is    becoming a major factor affecting the country's grain output.

He had planned to make a compromise，but        he changed his mind at the last minute. 

30．---- Do you think it's a good idea to make friends with your students?---- _____ , I do. I think it's a great idea.