Final answer:
The diameter of the Milky Way galaxy is about 100,000 light-years, making option D the correct answer for the size of our galaxy's visible disk.
Step-by-step explanation:
The diameter of the Milky Way galaxy is approximately 100,000 light-years. This measurement pertains to the visible disk of our galaxy, which is a vast collection of stars, gas, and dust. When considering options for the diameter of the Milky Way, it is clear that the correct answer is D. 100,000 light-years. The Andromeda Galaxy, our nearest large spiral neighbor and a galaxy similar to the Milky Way in terms of structure, is located about 2.4 million light-years from us. While we often refer to astronomical units (AU) when discussing distances within our solar system, light-years are a more appropriate measure for the vast scales between stars and galaxies.