What device connects a computer to the Internet using a phone line?

The device that connects a computer to the Internet using a phone line is a modem adapter. A modem (modulator-demodulator) converts digital signals from a computer into analog signals that can be transmitted over traditional phone lines, and vice versa. This allows the computer to send and receive data over the Internet through those phone lines.

The modem functions as a bridge between the digital world of computers and the analog world of telephone lines, enabling effective communication over distances traditionally limited by the telecommunication infrastructure. This capability is essential for dial-up internet connections, where the modem establishes a connection to an Internet Service Provider (ISP) using the phone line.

Other devices mentioned, such as SCSI adapters, wireless NICs, and RAID adapters, serve different purposes within a computer system and do not facilitate Internet connectivity over phone lines. SCSI adapters are used for connecting peripheral devices, wireless NICs enable wireless connectivity to networks, and RAID adapters manage multiple disk drives for redundancy and performance. Thus, the modem adapter is specifically designed for creating Internet connections through phone lines, making it the correct choice for this question.