All triangles are similar.
A triangle cannot have any reflex angle and hence reflex triangle is not possible.
In an Isosceles triangle, two sides are equal and hence two angles are equal but one side and angle is different which results triangles not to be similar.
In right angled triangle, it is not possible to have all the angles equal and hence they are not similar.
All Equilateral triangles are similar and this is because a property of equilateral triangles includes:
All of their angles are equal to .
Since every equilateral triangle’s angles are , every equilateral triangle is similar to one another.
It is due to this AAA Postulate.
Hence, the correct option is (D)