20. Polling topics can be as diverse as public policies, _________________________________, elections, ______________________ and academic research projects.

　　21. Old people are more _________________________________.

　　22. In order to prevent drug abuse, we can ___________ drug education programs to teach young people about the risks involved, toughen laws to prevent drug offenses, __________________

　　____________________ drug dealings.

　　23. War is a human __________. Millions of people die and fall apart ______________________ war.

　　24. __________________________________________________________________ the world is getting smaller and smaller.

　　25. Human beings can only ____________________________________________.

　　26. Economic growth cannot ________________________________________________of developing countries.

　　27. We are inhabitants of the earth only for a short time. We____________________________.

　　28. War is _________________________________.

　　29. To ___________ your memory, try to _________________________________.

　　30. The teacher tries to give a report to _________________________________.

　　Topic-related Paragraphs

　　1. Key Words: D.N.A.

　　Scientists say people and chimpanzees developed separately since they split_________________ about six million years ago. But studies have shown that chimpanzee genes _______________ _________________.

　　D.N.A. is made up of genes. Genes, like letters in words, carry a huge amount of information. These messages tell cells how to make all the _______________ for life.

　　2. Key Words: sub-prime mortgage crisis

　　American lawmakers and law enforcers are busy with _____________________________. Many of the recent problems were caused by sub-prime mortgages. These highly ______________ loans were marketed to risky buyers and then sold to _______________. But even homeowners with _______________ are having trouble with other new kinds of loans.

　　3. Key Words: child delivery

　　A new study in rural Nepal shows the value of washing hands with soap and water ________________________________. Researchers found that hand washing by birth attendants and mothers increased the chances that babies would ______________ their first month.