Mastering American English is the book of choice to accomplice the best understanding on all grammar rules. Words, sentences, and other elements, as well as their combination and interpretation are tough by this book in a very precise and American manner. This is the appropriate book to understand American English and the ideal book for foreigners who want to excel doing the TOEFL (Test of English as a Foreign Language). This book is prescriptive, descriptive and generative, therefore, nobody should have any problem to achieve good scores on English tests.