Analog communications: a modulation technique in which the amplitude of a carrier wave is varied according to some characteristic of the modulating (information) signal is known as:

Introduction / Context:
Modulation maps information onto a higher-frequency carrier to enable efficient transmission over a medium. Different modulation families alter different properties of the carrier—amplitude, frequency, or phase—each with characteristic performance and bandwidth trade-offs.

Given Data / Assumptions:

• The property varied is the amplitude of the carrier wave.
• The variation follows some characteristic of the modulating signal (e.g., its instantaneous value).
• We seek the standard name for this modulation method.

Concept / Approach:
When carrier amplitude varies in proportion to the message signal, the method is called Amplitude Modulation (AM). Angle modulation, by contrast, varies frequency or phase (FM/PM). “Aloha” is a random-access networking protocol, not a modulation; a modem is a device that performs modulation/demodulation but is not itself a modulation type.

Step-by-Step Solution:

Verification / Alternative check:
Classic broadcast radio on medium wave uses AM, where signal strength envelopes the carrier in proportion to audio amplitude.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing device names with techniques; mixing up amplitude vs. frequency/phase changes.

Final Answer:
Amplitude modulation.