Final answer:
An isosceles triangle has three sides, which is true for all types of triangles as they are three-sided figures with angles that add up to 180 degrees.
Step-by-step explanation:
An isosceles triangle is a type of triangle that has two sides of equal length. However, the question is asking how many sides a triangle has in general.
Regardless of the type of triangle, be it isosceles, equilateral, or scalene, every triangle is a three-sided figure lying on a plane, and the sum of the angles inside the triangle adds up to 180 degrees. Therefore, the correct answer to how many sides does an isosceles triangle have is D) 3.