Biology · Evolution

The following statements are potential explanations for the continued existence of genes that control eye development in eyeless cavefish: A. They have inherited these genes from their ancestors and these remain even though they no longer develop functional eyes. B. In case they return to the surface environment, retention of vision would be advantageous, so evolution consciously retains this trait for the future. C. Evolution can only lead to the gain of a trait, never the loss of a trait. D. These genes are retained because of the pleiotropic or combined role of these genes with other essential sensory developmental mechanisms. Which one of the following options represents the combination of correct statements?