Which type of provider offers internet access to users through phone lines?

The choice of Digital Subscriber Line (DSL) as the correct answer is well-founded. DSL is a technology that allows for high-speed internet access over traditional telephone lines, enabling users to connect to the internet while still using their phone line for voice calls. This characteristic distinguishes DSL from other types of internet providers, which may rely on different infrastructure.

In contrast, Direct Broadcast Satellite (DBS) provides internet access via satellite signals, often requiring a dish for transmission, and does not utilize phone lines. Cable Modem Providers utilize existing cable television lines to deliver internet service; while this method is also a form of broadband access, it is not reliant on phone line infrastructure. Fiber-optic internet service employs optical fibers to transmit data, offering faster speeds and higher bandwidth, but it does not operate over standard telephone lines.

Thus, DSL uniquely fits the criterion of delivering internet access through phone lines, making it the appropriate choice.