Final answer:
The correct statement is that translations and dilations preserve the orientation and proportionality of the sides, making the triangles similar with proportional corresponding angles.
Step-by-step explanation:
The statement that explains why triangles PQR and P"Q"R" are similar is that translations and dilations preserve angular measure and proportionality of sides, but not necessarily their length. Specifically, the answer is (a): Translations and dilations preserve orientation; therefore, the corresponding angles of PQR and P"Q"R" are proportional. A translation does not change the shape or angles of a triangle, it just moves it to a different location. A dilation increases or decreases the size of the triangle by a constant scale factor, which means all sides are multiplied by the same amount, maintaining their proportionality.