Final answer:
Hadrosauriformes includes the notable groups Iguanodontian and Dryosauridae, where Dryosauridae is often considered as a subset of the larger Hadrosauridae group within the 'bird hipped' Ornithischian dinosaurs.
Step-by-step explanation:
The Hadrosauriformes are a group of dinosaurs that are part of a larger clade known as the Ornithischian, or the "bird-hipped" dinosaurs. Within the Hadrosauriformes, there are indeed two notable groups: the Iguanodontian and Hadrosauridae. The Iguanodontian are a diverse group of herbivorous dinosaurs recognized for their complex dental structures, and the Hadrosauridae, commonly known as duck-billed dinosaurs, are known for their specialized teeth and dental batteries designed for processing plant material. Therefore, the correct answer to the student's question would be 'a. Iguanodontian and Dryosauridae,' provided that the 'Dryosauridae' is treated as a subset of the larger Hadrosauridae group, as the original 'Hadrosauriformes' option listed in 'd' is not appropriate since it's the overarching group, not a subgroup.