First the triangle 1 is translated in the right side to make triangle 2. Then the 2 triangle is reflected over to get triangle 3.
So, the correct answer is - translation, then reflection
In reflection transformation, the figure is reflected or flipped on a line called the axis of reflection or line of reflection. And translation means moving or shifting of a figure.
Triangle 1 - 2 shows a translation. A translation is when the triangle doesn't change shape, rotation, or size. It just slides. The 2- 3 shows a mirror image, which would be a reflection. Therefore, your answer is D.