When two voices sing exactly the same note simultaneously, the voices are singing
a. a doto.
b. in unison.
c. a cadenci.
d. a capella?

B. in unison
When two voices sing the exact same note at the exact same time, that is classified as singing in unison.

The answer is cave paintings

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.