I have found that though generally the book is quite useful for the explanations of Spanish grammar and exercises, there are a few mistakes on some of the exercises.One I found in the section of personal pronoums,(p.66) another one in the phrasing of an exercise which says tanto instead of "tan" (p.178). I have not used all the book yet, but possibly I could found still more errors. This is very irritating because, in my position, as a teacher, I must warn the students of these errors and this can cause confusion on their already insecure foundations of the Spanish language.I think the editors should have been more careful a should have made a more detailed study of the use of the language on some of the exercises.