In the adjoining figure, AB is the diameter of the circle with centre O. Two tangents p and q are drawn to th…

In the adjoining figure, $AB$ is the diameter of the circle with centre $O$. Two tangents $p$ and $q$ are drawn to the circle at points $A$ and $B$ respectively. Prove that $p\parallel q$. Further, a line $CD$ touches the circle at $E$ and $\angle BCD=110^{\circ }$. Find the measure of $\angle ADC$.