Answer:
A) dinosaurs, reptiles, and birds had a common ancestor
Step-by-step explanation:
The dinosaurs have not evolved as a separate phylum that has not close relations with other animals, but instead they share a common ancestor with the likes of the reptiles and the birds. The reptilians have actually emerged before the dinosaurs, but the dinosaurs managed to take up the top niches in the food chain after they appeared never the less. The birds on the other hand are actually an evolutionary product of the diversification of the dinosaurs. the birds have actually evolved from small bipedal dinosaurs, that over time started to take up new way of life and appearance in order to conquer the skies.