Final answer:
The clade of ornithopods with large, efficient tooth batteries for grinding plants is the Hadrosauridae, or duck-billed dinosaurs.
Step-by-step explanation:
The clade of ornithopods that had large, highly efficient tooth batteries for grinding plants is the Hadrosauridae, commonly known as duck-billed dinosaurs. These dinosaurs, which lived during the Late Cretaceous period, had hundreds of tightly packed teeth in their jaws that formed a continuous grinding surface. This adaptation allowed them to efficiently process tough plant material.