The correct answer is - A) The birds had beaks that were adapted for feeding differently.
The finches on the Galapagos Islands all derive from a small group of finches that were the same and managed to come to these islands. Over time, they started to develop numerous types of beaks, thus they started to diversify. The reason for this was that there were multiple free niches in the food chain on the Galapagos Islands, so the finches started occupying them. Some developed beaks that are more suitable for eating fruits, some that are more suitable for eating seeds and nuts, some that are more suitable for eating insects etc. All that different types of food choices contributed that they develop a beak type that will enable them to be more efficient in the consumption of their preferable food source.