Answer:
B.by contrasting web-based learning to books in terms of interactivity
Step-by-step explanation:
The third paragraph in the article, How E-learning is changing Education by Alicia Orlov explains the level of interactivity web-based learning affords, which is not obtainable with books. People can share ideas after taking courses online and also monitor their progress. People from different parts of the world can take same course and share their views among themselves. Teachers are not left out because they can improve their knowledge of certain subjects by taking courses on them online.
All of these means of interaction are not always obtainable with books.