The Sequence of Thermonuclear Fusion Processes Inside Massive Stars Can

The sequence of thermonuclear fusion processes inside massive stars can transform elements such as carbon and oxygen into heavier elements and generate excess energy until iron has been produced. Why is it NOT possible for fusion reactions to release energy from iron nuclei?

A) The electrostatic charge of iron nuclei is so great that other nuclei cannot approach closely enough to react with them.
B) Iron has the largest nucleus of all elements, and fusing other nuclei with iron actually reduces the size of the nucleus.
C) Iron is the heaviest naturally occurring element.
D) The protons and neutrons in an iron nucleus are so tightly bound together that fusing other nuclei with iron absorbs energy rather than releases it.