In the finite element method, which option is not a natural and direct formulation of momentum and continuity equations?

(a) Velocity-pressure formulation

(b) Penalty formulation

(c) Mixed formulation

(d) Lagrange multiplier formulation

I got this question by my school teacher while I was bunking the class.

My doubt stems from Penalty topic in portion Flows of Viscous Incompressible Fluids of Finite Element Method