Each group of four items includes a topic, a main idea, and two details that support the main idea. Click the main idea in each group.

a. The lion trainer enters the ring first, in full sight of the cats, to establish the ring as his territory.
b. Lion trainers working in circuses use basic principles of authority in training big cats.
c. By barking orders, stomping, and snapping a whip, the trainer shows his power.
d. Training lions.