9Teach with confidence, using the world'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 B provides six pages of additional practice for each unit in the second half of the Student's Book (units 9-16). 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.