Which of the following is a key protocol used for sending data over the Internet?

The correct answer is Internet Protocol, which is fundamental for data transmission over the Internet. Internet Protocol (IP) is responsible for addressing and routing packets of data so that they can travel across networks and reach their destinations. Each device on a network is assigned a unique IP address, acting like a home address that allows information to find its way to the right location. This protocol operates at the network layer of the Internet Protocol Suite and plays a critical role in establishing how data packets are sent and received across different networks.

Other options like FTP, HTTP, and SMTP are all protocols used for specific applications or types of data transfer, but they rely on the underlying Internet Protocol to function. FTP (File Transfer Protocol) is specifically used for transferring files between computers, HTTP (Hypertext Transfer Protocol) is the foundation of data communication for the World Wide Web, and SMTP (Simple Mail Transfer Protocol) is primarily used for sending emails. While all these are important for various internet services, they cannot operate without IP as the underlying framework that enables their communication.