Final answer:
C)polytonality.Using more than one key at the same time in music is called polytonality, a complex texture featuring multiple keys simultaneously, often found in 20th-century classical music compositions.
Step-by-step explanation:
Using more than one key at the same time in music is known as polytonality. Polytonality is a musical texture that involves multiple musical keys being played or sung simultaneously. It became a significant aspect of modern classical music in the 20th century through the works of composers such as Igor Stravinsky and Béla Bartók.
Unlike atonality, which avoids any sense of a key center, polytonality layers two or more distinct tonalities atop each other. This can create complex and rich harmonies, distinctive of early 20th-century music. Pentatonic refers to a five-note scale used across various musical traditions.
Polymeter, on the other hand, involves the use of two or more meters, or time signatures, concurrently.
Using more than one key at the same time is called polytonality. Polytonality is a musical technique where two or more different keys are used simultaneously in a composition. This creates dissonance and tension, as the keys clash with each other, but can also lead to unique and complex harmonies.