The objective of an astronomical telescope has large focal length and large aperture. Because the lens used is a convex lens, the magnification of an astronomical telescope is directly proportional to the focal length of the objective lens.
This large aperture also contributes to the better quality and visibility of the images. Thus, it provides better resolution.

Due to large focal length of the objective, it covers large area which ensures better light gathering power.
Thus, all options , and are correct.