Answer:
A. during a supernova
Explanation:
The most common elements, like carbon and nitrogen, are created in the cores of most stars, fused from lighter elements like hydrogen and helium. The heaviest elements, like iron, however, are only formed in the massive stars which end their lives in supernova explosions.
Heavy elements might be formed when lighter elements combine with neutrons in dying low-mass stars. Other possible sources of heavy elements include powerful supernova explosions and the collision of two neutron stars.
