Help me please. Questions from TOEFL test

I don't know how to correct.

1. A chunk of uranium the size of a softball can release more energy than a trainload of coal that weighs 3 million times so much.
2. The piano as it is known today represents a long series of experiments extended back to the year 1711, or perhaps even earlier.
3. Education in the United States is overseen by local school districts, which follow regulations mandated by their respective state government.
4. Today’s fashion designers must consider both how much a fabric cost and how good it wears
5. An audience is different from a crowd in that it refers to people who gather for the purpose of listening or observing some proceedings in accordance with a program set in advance.
6. Timothy Shay Arthur did so poor in school but became an avid reader and in the process seriously damaged his eyesight.
7. Yearning for a truly representative art form of the Americas, the art world of the 1920’s looked hopeful to the three popular Mexican mural artists of the day.
8. No matter how cautious snowmobiles are driven, they are capable of damaging the land over which they travel.
9. Elaine Kim’s study creates an insight on the contributions of Asian-American women to the economic and cultural development of the U.S.
10. A possible first step in developing a nonsexist vocabulary with which to discuss about the works of the nineteenth-century writer Elizabeth Gaskell would be to cease referring to her as “Mrs. Gaskell”.
11. An ingenious system for carrying mail, the Pony Express was existing only briefly before the telegraph system made it obsolete.

1.D 2.C 3.D 4.D 5.B 6.A 7.C 8.B 9.A 10.C 11.B