In this paper we study the boundary exact controllability for the equation $$\frac{\partial }{\partial t}\left(\alpha \left(t\right)\frac{\partial y}{\partial t}\right)-\sum _{j=1}^n\frac{\partial }{\partial x_j}\left(\beta \left(t\right)a\left(x\right)\frac{\partial y}{\partial x_j}\right)=0\text{in}\Omega \times (0,T),$$ when the control action is of Dirichlet-Neumann form and $\Omega$ is a bounded domain in $R^n$. The result is obtained by applying the HUM (Hilbert Uniqueness Method) due to J. L. Lions.