Final answer:
Complex tones can be produced by different sources such as musical instruments, bird songs, and human speech sounds.
Step-by-step explanation:
All of the answers are correct. Examples of complex tones include notes played by musical instruments, bird songs, and human speech sounds. In music, complex tones are produced when the fundamental frequency and overtones are present simultaneously in a variety of combinations. For example, middle C played on a trumpet has a different sound than middle C played on a clarinet. These differences in overtones and their mix of intensities give different musical instruments and human voices their distinct characteristics.