Book excerpt: Interchange Fourth Edition is a four-level series for adult and young-adult learners of English from the beginning to the high-intermediate level. Interchange Fourth Edition Online Workbook, Intro provides additional activities to reinforce what is presented in Student's Book, Intro. The Online Workbook includes activities which correspond to each Student's Book unit; instant feedback for hundreds of activities; clear, easy-to-follow navigation; additional audio practice; and simple tools to monitor progress.