ANS:D - all the above.

1. The diameter of the aperture: The resolving power of a telescope is primarily determined by the diameter of its aperture. The aperture is the opening through which light enters the telescope. A larger aperture allows more light to enter the telescope, which in turn increases the telescope's ability to resolve fine details and distinguish between closely spaced objects in the sky. This is because a larger aperture collects more light and produces a sharper image.
2. The pupil aperture of the eye: The pupil aperture of the eye refers to the opening in the iris through which light enters the eye. While the pupil aperture of the eye does not directly affect the resolving power of a telescope, it does influence the amount of light entering the eye when observing through a telescope. A larger pupil aperture allows more light to enter the eye, resulting in brighter images and potentially improving the observer's ability to perceive details.
3. The diameter of the object glass: The diameter of the object glass, which is typically the same as the aperture, also plays a crucial role in the resolving power of a telescope. As mentioned earlier, a larger diameter allows more light to enter the telescope, thereby enhancing its resolving power. The object glass is the primary lens or mirror in the telescope that gathers and focuses incoming light onto the eyepiece.