Question

Tina described four triangles as shown below:

Answer 1

All triangles are unique. 
The question should read, which two of the 4 given triangles are similar.the intended answer is likely triangle D, because there are infinitely many different triangles described by D, namely all equilateral triangles.

Answer 2

Answer:

Triangle D is not a unique triangle.

Step-by-step explanation:

Triangle A:  All sides have length 12 cm.

such a triangle will be a unique triangle and it will be an equilateral triangle.

Triangle B: Two sides have length 10 cm, and the included angle measures 60°.

Such a triangle will also be unique because with the help of the given angle measure and and the angles opposite to equal sides are equal we can find the measure of those two angles.

and hence we can construct a triangle with the help of these information.

Triangle C:  Base has length 15 cm, and base angles measure 40°.

Such a triangle will also be unique as a unique triangle could be constructed with the help of these information.

Triangle D: All angles measure 60°.

Such a triangle will be an equilateral triangle but we can't say it will be unique as we can construct infinite number of triangles with different side lengths.

Hence such a triangle is not unique.