Irregular Plurals

Lesson from the Shenzhen Daily: http://szdaily.sznews.com/html/2012-04/12/content_2000861.htm

Practice the conversation; study the vocabulary; then discuss the questions with a friend in English.

Questions:
1. What are the "four categories" of irregular plurals used by Lederer?
2. I have given eleven more categories of irregular plurals ("-fe changes to -ve," etc.) Can you think of more examples for each category?
3. Do the "little test" at the end of the article.