Correct nonessential elements and punctuation are in bold.

1. Patterson Tower, the recently completed office building, is a monument to concrete ugliness.

2. The movie that I wanted to see is no longer playing. (correct)

3. Each person who enters the contest must send in two box tops. (correct)

4. John decided, nonetheless, not to buy the car.

5. The Mississippi River, which once flowed north into Hudson Bay, flows south into the Gulf of Mexico.

6. Your cat, watching the dog intently, walked carefully away.

7. The cat that was watching the dog most intently walked carefully away. (correct)

8. TV commercials, sometimes the most entertaining parts of a program, are essentially flashy corporate propaganda.

9. The dam project, which many in the government consider to be a sign of national strength, will destroy hundreds of villages and vast areas of wildlife habitat along the river banks.

10. The free-jazz musician Sun Ra claimed to be from Saturn. (correct)