Darwin theorized that the finches on the galapagos islands were related because the finches
a) had the same size beaks.
b) ate the same kind of food.
c) sang the same kind of song.
d) were the same size and color.

D) were the same size and color

Explanation:

Darwin during his voyage to the Galapagos Islands, he discovered that virtually all the finches on the different islands of the Galapagos appear similar in size and color, and one major remarkable differences among these finches that are found in the different islands of the Galapagos is the difference in their beak shape and size. Although they appear similar in body size and color, their beak shape and size differ, which is said to have become adapted to the different type of food found in each Island.

However, the similarity in the body size and color of the finches made Darwin to theorized that the finches on the Galapagos Islands were related, and that they descended from a common ancestor.