Here are the correct answers for each numbered blank in the passage:

1. **D. Which** - This is the correct choice because "which" introduces a non-defining relative clause that provides extra information about the e-reader.

2. **C. Convenient** - This word best describes e-readers compared to printed books, as they offer the convenience of storing many books in one device.

3. **D. Printed book** - The context suggests that the comparison is with a traditional printed book, highlighting features that e-readers have that traditional books do not.

4. **C. In** - This preposition is the most appropriate in the phrase "interested in e-books".

5. **C. Although** - This word indicates a contrast, suggesting that even though e-readers may have become less popular, they are still used by many book lovers.

So the answers are:
1. D
2. C
3. D
4. C
5. C