Final answer:
The extremely broad sacrum of Scelidosaurus suggests affinities with the ankylosaurs. Therefore, the correct option is A.
Step-by-step explanation:
The extremely broad sacrum of Scelidosaurus suggests affinities with the ankylosaurs. The sacrum is a triangular bone at the base of the vertebral column, and its shape and size can provide clues about the evolutionary relationships of an organism. Ankylosaurs are a group of armored dinosaurs characterized by their broad and low-slung bodies, which is similar to the broad sacrum of Scelidosaurus. Based on this anatomical similarity, it is likely that Scelidosaurus is closely related to ankylosaurs.