Why does a diamond change directly from a solid state to a gaseous state?

Diamond changes directly into gaseous state from solid state because it undergoes sublimation. As the structure of the diamond contains a network of solid which is formed from carbon atoms, which makes diamond a strongest solid which does not undergoes melting process to form liquid state instead it undergoes phase transition directly from solid to gaseous state. It has cubic crystal structure in which it has a repeating pattern of 8 atoms.

the answer is either b or c