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The Andromeda Galaxy, also known as Messier 31, NGC 224, is a spiral galaxy approximately 2.5 million light-years away from Earth. It is in the constellation Andromeda, and it is the nearest spiral galaxy to our own, the Milky Way. Both the Milky Way and the Andromeda Galaxy are members of the Local Group, which also includes the Griangulum Galaxy, among others. Until recently, it was believed that the Andromeda Galaxy had the greatest mass of the three Galaxies in the Local Group, but recent findings suggest that the Milky Way has the most dark matter out of the three, and this fact may suggest that in fact the Milky Way is the most massive.
If the next sentence in the passage were, "Scientists are still uncertain, and more research is needed to settle the matter," referring to the fact that scientists are uncertain about the relative masses of the Milky Way and the Andromeda Galaxies, then which of the following should also be included in the passage to help place that new sentence into context.
A.A discussion about the philosophical arguments regarding the masses of the two galaxies.
B.A detailed and intricate scientific account, with the inclusion of physics formulas, of the current research studies that are the result of the controversy.
C.A discussion about the distance between the Andromeda and Milky Way Galaxy.
D.A brief overview and summary of the key research projects that have provided evidence about the dark matter in the Milky Way and the overall mass of the Andromeda Galaxy.
E.A discussion about the number of stars and amount of dark matter in the Orion Constellation.
