Réponse:

Sure! Here are some sentences using "there + be" to describe future cities with specific features:

1. In the future, there will be floating cities where buildings hover above the water, creating a mesmerizing sight.

2. There will be city fish swimming gracefully in the canals of these futuristic urban centers, adding a touch of natural beauty.

3. Around these floating cities, there will be lots of innovative structures designed to blend seamlessly with the surrounding environment.

4. In these future cities, there will be large forest boat trees that serve as green spaces and provide a breath of fresh air in the bustling metropolis.

5. Everywhere you look, there will be innovative buildings showcasing cutting-edge architecture and sustainable design principles.

6. The future cities will have an abundance of swimming areas, offering residents and visitors the opportunity to cool off and enjoy water-based activities.

7. Picture a future city with large forest boat trees scattered throughout, creating a harmonious blend of nature and urban infrastructure.

8. In these futuristic urban centers, there will be floating gardens and parks, providing serene oases amidst the bustling city life.

9. Imagine walking through these future cities and encountering vibrant underwater ecosystems teeming with colorful marine life.

10. The future cities will feature an array of unique transportation systems, including water taxis and floating walkways, making commuting a truly memorable experience.

Remember, these sentences depict imaginative descriptions of future cities and do not necessarily reflect current technological capabilities.