Question

You probably know sharks have very sharp teeth but did you know they never run out of them if a shark loses a tooth another moves forward from within the sharks jaw where it keeps a nearly unlimited supply of replacement teeth this is a phenomenon unique to the shark No other animal in the world had teeth quite like the sharks a shark can go through as many as 20,000 teeth in its lifetime
Question 1 what is the main idea
Question 2 concluding sentence

Answer 1

Main idea: A shark's teeth are constantly being replaced

Concluding sentence: No other animal in the world had teeth quite like the sharks a shark can go through as many as 20,000 teeth in its lifetime.