The correct option is D Diamond, Graphite
A network solid or covalent network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material.
Diamond :
It has a crystalline lattice in which each carbon atom is sp3 hybridized.
Each carbon atom is linked to four other carbon atoms and the C-C bond length is 154 pm
The structure extends in space and produces a rigid 3-D network of carbon atoms with directional covalent bonds throughout the lattice.
Graphite has a layered structure held by van der Waals forces and distance between two layers is 340 pm.
Each layer is composed of planar hexagonal rings of sp2 hybridized carbon atoms.
Hence both diamond and graphite consists of only network solid