How do you know which shark is harmless and which shark is dangerous?

a shark looks like a gigantic fish, but with teeth. sharks are very well known predators around the Atlantic Ocean, Pacific Ocean, and some lakes, but people are taking care of that. sharks come in all different shapes and sizes, big, small, long, or short. the most well known shark is the Great White shark, about 1,000 deaths are reported every year for great white attacks. some people say that there is a prehastoric shark, called Megaladon, apparently, it is about 3 school busses long, and can kill a Blue Whale. if you want to look at sharks, goto DiscoveryChannel.com.