Final answer:
The correct answer to the student's question is 'b. Archaeopteryx', which is considered the earliest and most well-known primitive bird and a transitional fossil between non-avian dinosaurs and birds.
Step-by-step explanation:
The question pertains to the classification of birds or feathered dinosaurs. Among the options provided, b. Archaeopteryx is considered the earliest and most primitive known bird. The Archaeopteryx lived during the late Jurassic Period around 150 million years ago. It is often cited as a transitional fossil between birds and dinosaurs due to its blend of avian and reptilian features. The Archaeopteryx had feathers and wings but also had teeth and a long bony tail, traits typically found in non-avian dinosaurs.
It is worth noting that Neornithes refers to the modern birds that constitute most of the bird species alive today. Enantiornithes were a group of prehistoric birds which are now extinct. Paleognathae, on the other hand, is a clade that includes the extant ratites, such as ostriches and emus, and the tinamous.