What method gives each call a special code and spreads it out over available frequencies?

The correct answer is C. CDMA (Code Division Multiple Access).

CDMA is a method used in wireless communication that allows multiple signals to occupy the same transmission channel by assigning a unique code to each call. This unique code spreads the signal over a wide frequency range, allowing multiple users to share the same frequency band simultaneously without interference, which enhances the overall capacity of the network.

If you have more questions or need further clarification, feel free to ask!