From his observations of cannon drilling, Count Rumford concluded that heat could NOT be a form of

Akinetic energy.
Bpotential energy.
Cmatter.
Dradiation

Verified Answer :

From his observations of cannon drilling, Count Rumford concluded that heat could NOT be a form of C. matter.
Although all matter contains heat energy, heat itself is not a form of matter, but just one of its integral parts.

Matter is your answer.