ld's favorite English course. Interchange is a four-level, American English course that has been used by over 50 million students worldwide. This Intro level Workbook A provides six pages of additional practice for each unit in the first half of the Student's Book (units 1-8). The workbook helps recycle and review language by providing additional practice in grammar, vocabulary, reading, and writing. It is appropriate for in-class work or can be assigned as homework.