Fundamental particles are elementary, not composed of smaller particles.

Steps:

• Define fundamental particles as elementary constituents in the Standard Model, with no substructure.
• Identify A: charm quark as a basic quark flavor, not composite.
• Identify B and C: electron and neutrino as leptons without internal parts.
• Identify D: neutron as a hadron built from quarks, thus composite.

Why D is correct:

• The neutron is a baryon composed of one up quark and two down quarks, bound by the strong nuclear force, per quantum chromodynamics.

Why the others are wrong:

• A: Charm quark is an elementary particle in the Standard Model's quark sector.
• B: Electron is an elementary lepton with no subcomponents.
• C: Neutrino is an elementary lepton, interacting only via the weak force.

Final answer: D