Exampe:
Let $\Omega$ be a disc of radius 1 centered in the origin,
and let $D$ be a disc of radius 0.5 centered in the origin as well.
Is it possible to solve
$$-\Delta u = 1 \quad \text{in } \Omega\,, \quad u = 0 \quad\text{on } \partial\Omega\,,$$
using first order continuous Lagrangian finite elements in $\Omega\setminus D$ and
second order continuous Lagrangian finite elements in $D$?