See the picture attached to better understand the problem
we know that
A quadrilateral is called Cyclic quadrilateral <span>if its all vertices lie on the circle.
</span><span>The opposite angles of a Cyclic - quadrilateral are supplementary
</span>so
∠A+∠C=180°
and
∠B+∠D=180°
therefore
the answer is
<span>C) The sum measure of ∠B and ∠D equals 180°</span>
we know that
A quadrilateral is called Cyclic quadrilateral <span>if its all vertices lie on the circle.
</span><span>The opposite angles of a Cyclic - quadrilateral are supplementary
</span>so
∠A+∠C=180°
and
∠B+∠D=180°
therefore
the answer is
<span>C) The sum measure of ∠B and ∠D equals 180°</span>