Final answer:
Angling the central ray (CR) or the object can result in projectional distortion, causing elongation or shortening of the object's image, while angling the image receptor adjusts the image plane without causing such distortion. Therefore, the correct answer is b. 1 and 2 only.
Step-by-step explanation:
The question relates to the principles of image projection in physics, particularly with an emphasis on the magnification of objects when the imaging system parameters are altered. When considering the elongation of an object when it is positioned horizontally, three factors can affect the image size: 1) angling the central ray (CR), 2) angling the object, and 3) angling the image receptor. Angling the CR or the object can create a distortion known as projectional distortion, which can result in the apparent elongation or shortening of the object image based on the angulation relative to the image receptor. However, angling the image receptor itself does not create projectional distortion, but rather adjusts the plane where the image is captured, potentially affecting the sharpness or focus of the resultant image. Therefore, the correct answer to the question of which options cause elongation is options 1 and 2, so the answer would be b. 1 and 2 only.