In data communication, what is the main function of a modem when connecting a digital computer to conventional analog telephone lines?

Introduction / Context:
This question addresses the basic role of a modem in computer networks and communication systems. Before broadband and direct digital connections became common, dial up modems were widely used to connect computers to the internet over ordinary telephone lines. Understanding what a modem does with signals is still important for fundamental networking knowledge.

Given Data / Assumptions:

• The modem connects a digital computer to analog telephone lines.
• Telephone lines traditionally carry analog signals.
• The computer produces and understands digital signals only.
• Options describe converting only in one direction or in both directions, plus unrelated functions.

Concept / Approach:
The word modem comes from modulation and demodulation. A modem converts, or modulates, digital signals from a computer into analog signals suitable for transmission over telephone lines. At the receiving end, another modem demodulates the analog signals back into digital form for the receiving computer. Both operations are necessary for two way communication. A device that only converts in one direction would not support full communication. Options that describe unrelated functions such as printing or amplification are not correct.

Step-by-Step Solution:
Step 1: Note that computers generate digital signals, while conventional telephone lines are designed for analog voice signals. Step 2: For a computer to send data over a telephone line, the digital data must be converted into analog form. This process is modulation. Step 3: At the receiving end, the analog signal must be converted back into digital form for the other computer. This process is demodulation. Step 4: A modem is the device that carries out both modulation and demodulation, which is why the name combines the two terms. Step 5: Option a mentions only translating analog signals into digital, which describes only the demodulation part and ignores modulation. Step 6: Option b describes only the modulation part, converting digital to analog, and again does not mention the reverse process. Step 7: Option c correctly states that the modem performs both modulation and demodulation between digital and analog signals. Step 8: Options d and e talk about amplifying telephone handsets or printing hard copies, which are not the core functions of a modem.

Verification / Alternative check:
Any introductory networking textbook defines a modem as a device that converts digital data from a computer into analog signals suitable for transmission over voice grade lines and then converts incoming analog signals back into digital data. They specifically highlight the combined role of modulation and demodulation. The presence of both functions is what enables bi directional communication over traditional telephone networks using digital computers.

Why Other Options Are Wrong:
Options a and b describe only part of what a modem does and therefore are incomplete. A real modem must handle both directions to support sending and receiving data. Option d is unrelated, as amplifying sound is the job of audio equipment, not modems. Option e describes a printer, which is not a communication device at all.

Common Pitfalls:
Students may incorrectly pick an option that sounds technical but only mentions one direction of conversion. To avoid this mistake, always remember that communication is two way. A device that connects two different signal types must be able to convert in both directions. The name modem itself is a reminder of this dual role, which can help you recall the full definition during exams.

Final Answer:
A modem works by performing both modulation and demodulation between digital computer signals and analog telephone line signals.