All …. Triangles are similar.
A. Right angled
B. Isosceles
C. Equilateral
D. Reflex

Hint: Here we have to find out which types of triangles are always similar. First, we will define a similar triangle. Then we will check each option one by one and find which option satisfies the definition of a similar triangle.

Complete step-by-step answer:
Similar triangles are those whose corresponding angles are congruent and the corresponding sides are in proportion.
As we know that corresponding angles of an equilateral triangle are equal, so that means all equilateral triangles are similar.
We can’t say this for a right angle triangle as its one angle is \[{90^ \circ }\] and the other two angles can be different or similar.
Similarly, for isosceles triangles the two corresponding angles are the same but the third one is different.
There is no triangle which is termed as a reflex triangle, rather it is a type of angle. When the measure of the angle is greater than \[180^\circ \] but less than \[360^\circ \] is termed as reflex angle.

Hence, option (C) is correct.

Note:
Similar triangles are the triangles having the same shape but different sizes. The symbol used to denote the similarity of triangles is \[ \sim \]. There are many ways to determine whether two triangles are similar or not which are defined as follows:
1. If two angles of one triangle are equal to the other triangle they are similar.
2. If two sides are in the same proportion in both triangles and the angle formed by the two sides are also the same then they are similar triangles.
3. If all three sides of the two triangles are in proportion they are similar triangles.