Answer: Rotations, reflections, translations (A, C, and E)
Imagine you had a camera aimed at a triangular figure on a piece of paper. If you rotate the camera, then the image of the triangle appears to rotate. In reality it's the other way around. What this means is that the triangle is not changing at all. It keeps the same size, shape, area, perimeter, etc. This applies to when the camera pans left or right, ie shifts from side to side. The triangle will translate but again the triangle isn't changing at all. It's merely an illusion. Reflections are the same way. Imagine having a piece of glass or a mirror that reflects the image which is an identical copy; although everything is flipped.
Dilations are not isometries because the image is a different size then the pre-image. The same shape is maintained though. Note: the scale factor must be some number other than 1.
another note: "isometry" breaks down into "iso+metry" with "iso" meaning "same" or "equal", and "metry" meaning "measure". So if you had 2 identical yard sticks, then they are isometrical or equal in length.
