Concept:A tangent to a circle is perpendicular to the radius drawn to the point of contact, forming a 90∘ angle.Explanation:In the given triangle, m and n are two angles, and the third angle is the right angle formed by the radius and the tangent.So, the three angles of the triangle are m, n, and 90∘.Using the sum of angles in a triangle:m+n+90∘=180∘m+n=180∘−90∘m+n=90∘Answer:B. 90∘