Hexagonal Boron Nitride (h-BN), often represented by the formula BN, has a layered structure similar to graphite, hence it is known as "inorganic graphite". It consists of hexagonal rings of alternating boron and nitrogen atoms. Although the formula (BN)₃ is not standard and often represents a trimer unit, among the given options, it is the only one related to Boron Nitride. Borazine (B₃N₃H₆) is known as "inorganic benzene" due to its cyclic structure and aromatic properties, not inorganic graphite. Si₆ is a silicon cluster, and Si₃N₄ is silicon nitride, a ceramic material, neither are inorganic graphites. Therefore, assuming (BN)₃ refers to a form or constituent unit of Boron Nitride, Option A is the intended answer.