Why did theorists find it necessary that organum include oblique and contrary motion rather than limiting it to strict parallel motion?

For the first time, the electronic synthesizer allowed composers to create

a. stereo and surround sound. b. music without performers. c. the sound of pure vibration. d. a natural echo chamber.

What is the instrument heard in the performance of this selection?

a) synthesizer b) harpsichord c) fortepiano d) organ