Final answer:
Option A (True) is correct as it was widely accepted that dinosaurs were reptiles until the 1990s. Dinosaurs, which emerged around 225 million years ago, were integral to the reptilian-dominant Mesozoic Era, also known as the Age of Reptiles.
Step-by-step explanation:
The view that dinosaurs were reptiles was indeed the predominant scientific view until the 1990s, which makes option A (True) the correct answer to the student's question. Dinosaurs, which appeared around 225 million years ago, were a diverse group of terrestrial reptiles and not lizards. They exhibited a unique upright posture, unlike that of lizards, and were part of a larger group of sauropsids that evolved into various reptile classes. Their dominance during the Mesozoic Era, also known as the Age of Reptiles, ended with the mass extinction at the end of the Cretaceous period, about 65 million years ago.
The Mesozoic Era is renowned as the Age of the Dinosaurs due to their evolutionary radiation filling numerous terrestrial niches. It was only after the Cretaceous-Paleogene extinction event, which claimed the majority of dinosaur species along with various other forms of life, that mammals began to take on a more dominant role in the early Cenozoic Era.