Sure, here are the completed sentences:

1. The pen is 4$. The book is 7$.
- The pen is **less expensive than** the book. (expensive)
- The book is more expensive than the pen. (expensive)
- The pen is cheaper than the book. (cheap)

2. Long is not as careful as Tam.
- Long is **less careful than** Tam. (careful)
- Tam is **more careful than** Long. (careful)
- Long is **not as careful as** Tam. (careful)

3. This street is not so crowded as that one.
- This street is **less crowded than** that one. (crowded)
- That street is **more crowded than** this one. (crowded)