These may not be the only changes that do the job. If you are uncertain (or disagree!) with any of them, let me know. But keep in mind that simply considering the possibilities is already useful.
1. Her dress was pink.
2. That society is interesting.
3. Having just finished college [[needed to establish authority]], I can testify that mental discipline is the greatest asset a student can have.
4. The Encyclopedia Britannica, with almost five pages on Shelley, is probably the best source.
5. Ellen looked sick.
6. I think that he is wrong.[["He is wrong" doesn't express the tentative nature of the statement]]
7. Most of the story dealt with Robert Peel's very active political life.
8. A Farewell to Arms was Hemingway's first commercially successful novel.
9. Crowds of people were milling about. [[or "Crowds were milling about."]]
10. He voted for the independent candidate because she had an antiwar record.
11. Early in his career, Pete Rose met a coach who urged him to analyze his motions at the plate.