Explanation:

All the listed services — Twitter, Skype, and Gmail — are built on cloud-computing technology. Here's how:

• Twitter: Uses cloud infrastructure to scale, store tweets, and manage millions of concurrent users.
• Skype: Operates over the internet using cloud servers for voice/video calls and messaging.
• Gmail: A Google service entirely cloud-based, offering email access from anywhere via web and mobile apps.

These services rely on cloud computing for scalability, availability, storage, and performance.