Which Greek prefix means 'sound'?

The Greek prefix that means 'sound' is indeed phono-. This prefix is derived from the Greek word "phōnē," which translates to "voice" or "sound." It is commonly used in terms related to sound and auditory phenomena, such as "phonetics," the study of the sounds in human speech, and "telephone," a device that transmits sound. This prefix's application illustrates its direct connection to sound and auditory experiences, making it the correct answer.

The other prefixes have distinct meanings that do not relate to sound; for example, therm- relates to heat, theo- pertains to God or religion, and polis refers to a city or community. Understanding these meanings can help in distinguishing between them and recognizing the specific role of phono- in language and terminology.