Teach 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 B Student's Book with ---- includes access to an ---- with audio. It has Units 1-8, progress checks, and a Grammar Plus section to ensure students receive all the practice they need. Inside each book is a single-use code for the ---- with audio, which is mobile-friendly and can be used on a smartphone, tablet, or computer.