Question

Macy described four triangles as shown below:

Answer 1

Triangle-A is not "unique".
All of its angles are equal (60° each), and all of its sides
have the same length, but that length can be anything ...
1 millimeter, 1 light-year ... anything.

Each of the other choices can only be 1 triangle.
For each one, we can find the size of every angle,
and we can also find the length of every side.