Right choice is (a) Isosceles
The explanation: As we know that there are three types of triangle
(i) Equilateral Triangle: All sides are equal in length and all the angles measure 60°
(ii) Isosceles Triangle: Two sides are of equal length and the corresponding base angles would be of equal measure.
(iii) Scalene Triangle: All three sides of the different lengths and all the angles are of different measures.