The defining property of an isosceles triangle is that it has at least two sides of equal length.
• All 3 angles the same — this is equilateral, not the definition of isosceles.
• 2 sides are of the same length — TRUE. This is the definition.
• All sides different — FALSE (that is a scalene triangle).
• Must have a right angle — FALSE (only right-angled isosceles triangles have one).
Final Answer: B: 2 sides are of the same length