Here are the completed sentences:

1. The car and the motorcycle have the same speed.
- The car runs **at the same speed as the motorcycle**.

2. The elephant's weight is double that of the rhinoceros.
- The elephant weighs **twice as much as the rhinoceros**.

3. That restaurant has a larger menu selection than any other in town.
- That restaurant has **the largest menu selection** in town.

4. As you study more, you'll find yourself becoming more knowledgeable.
- **The more** you study, **the more** knowledgeable you’ll become.

5. The movie was more interesting than the book.
- The book was **less interesting** than the movie.

6. This laptop is the most powerful I’ve seen.
- This laptop is **more powerful than** any other laptop I’ve seen.

7. The library has multiple times as many books as the bookstore.
- The library's book collection is **several times larger than** that of the bookstore.

8. You will have more money in the future as you save more.
- **The more** you save, **the more** money you’ll have in the future.

9. His house and our house are the same in size.
- His house is **as large as** ours.

10. No other team in the league is as successful as ours.
- Our team is **more successful than** any other team in the league.

11. This book weighs triple the weight of that one.
- This book weighs **three times as much as** that one.

12. Her sister is not as smart as she is.
- She is **smarter than** her sister.

13. This cake is much sweeter than the last one.
- The last cake was **not as sweet as** this one.

14. This is the most vibrant painting in the gallery.
- **No painting is as vibrant** as this one.

15. This city's population is only half as large as that one.
- The population of that city is **twice as large as** this one.