References

1. Algeo, John; Pyles, Thomas (2009). The Origins and Development of the English Language .

[https://books.google.com.ua/books?id=znFmBZ2D8rEC&pg=PA1&hl=ru&source=gbs_toc_r&cad=4#v=onepage&q&f=false]

2. http://grammar.about.com/od/il/g/irregularvterm.htm

3. http://grammar.about.com/od/grammarfaq/f/weakstrongverbsfaq.htm

4. "English Grammar for Dummies" by Geraldine Woods. Published by Wiley Publishing Inc., New York, 2002.

5. https://en.wikipedia.org/wiki/English_irregular_verbs

6. http://english.stackexchange.com/questions/137348/why-are-so-many-important-verbs-irregular

7. http://www.usingenglish.com/reference/irregular-verbs/

8. http://blogs.discovermagazine.com/notrocketscience/2009/09/29/the-evolution-of-the-past-tense-how-verbs-change-over-time/#.VxUjODCLSL9

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