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 Level 1B Student'S Book With Digital Pack Has Units 9-16, 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 Digital Pack To Access The Digital Workbook With Hundreds Of Self-Graded Exercises, Audio, Videos, And An . The Digital Pack Is Mobile-Friendly And Can Be Used On A Smartphone, Tablet, Or Computer.