Final answer:
Modems are important nowadays mainly because of wireless transmission, which allows devices to connect to the internet wirelessly. (option C is the correct answer)
Step-by-step explanation:
The main reason why modems are important nowadays is C. Wireless transmission. Modems enable devices to connect to the internet wirelessly, allowing for convenient and widespread access to online resources. Through wireless transmission, modems can connect to Wi-Fi networks, cellular data networks, and other wireless technologies to provide internet connectivity.
Wireless transmission (C) involves the use of radio waves to transmit data, and modems are essential components that modulate and demodulate signals for effective communication. Spread spectrum transmission (D) is a technique used within wireless communication, making the "spread" of signals over a broad frequency band, and modems are integral in implementing this technology.
Modems are pivotal in enabling wireless transmission, supporting the seamless exchange of data between devices through radio waves, and are central to the functionality of contemporary communication systems.