A quadrilateral ABCDABCDABCD is inscribed in a circle. If ∠A=100∘\angle A = 100^{\circ}∠A=100∘ and ∠B=80∘\angle B = 80^{\circ}∠B=80∘, what is ∠C\angle C∠C?
80^{\circ}
90^{\circ}
100^{\circ}
120^{\circ}