Which of the following statements about triangles is true?

• A. All triangles have two sides.
• B. All equilateral triangles have three sides.
• C. All scalene triangles have equal angles.
• D. All right triangles are equilateral.

Answer: (B)

The statement that all equilateral triangles have three sides is true because the definition of an equilateral triangle is precisely that it has three sides that are all of equal length. By definition, a triangle is a polygon with three edges and three vertices, so any triangle, including equilateral triangles, will always have exactly three sides. This characteristic distinguishes triangles from other polygons, such as quadrilaterals, which contain four sides.

In contrast, triangles with different properties, such as scalene (which have all sides of different lengths and angles of different measures) or right triangles (which have one angle that is exactly 90 degrees), still fundamentally have three sides, but they do not apply to this definition. Hence, the truth of the equilateral triangle having three sides aligns perfectly with the geometric definition of all triangles.