Performance of a single melodic line by more than one instrument or voice is described as playing or singing in: select one:
a. harmony
b. imitation
c. unison
d. counterpoint

C) Unison.

Explanation:

In the context of music, unison is the absence of a gap between two sounds emitted simultaneously, is the same sound, or exactly the same note played by more than one transmitter, or more than one voice singing the same notes at the same level of pitch, sounding at the same time. The song sung in unison is called monophonic.

While unison is represented by the same sound, the canon is a musical form based on imitation, that is, when a melody is performed in two or more different parts, repeating itself indefinitely.