Read the passage below carefully, and then choose the best answer:
Piranhas on Parade
With the exception of whales and sharks, fish are generally considered to be harmless creatures. The thought of a small fish hurting anyone is almost laughable. However, piranhas are an exception to this rule. They frequently attack in groups and in some cases they can cause great bodily harm. Most piranhas are under 25 centimetres long, but don’t let their size fool you. Unlike most fish, they have two rows of razor-sharp teeth. Their triangular shape makes them perfect for puncturing and shredding whatever they bite. Although piranhas usually swim alone, they also hunt in school of 1,000 fish or more, which greatly multiplies the damage they are capable of. As small fry, they feed of vegetables and plankton until they can tolerate meat. In terms of flesh, they will eat any animals or fish that enters their territory when swimming in schools, even humans. In some cases, hungry piranhas will even go after each other if they are really desperate for a snack. However, the danger they present to humans is often exaggerated. In Hollywood films, piranhas are often portrayed as vicious destroyers who love to eat people. Some rumours even developed that schools of hungry piranhas will quickly kill and consume humans in a matter of seconds. In reality, the majority of these attacks only consist of a few painful, but non-life threatening bites to the person. However, that is not always the case. A recent attack on December 25, 2013 in Argentina left at least 60 people injured. Victims were wading in a river when a sudden attack began. Local police believe that some local debris left floating by fishermen brought the piranhas to the area. Many swimmers left the water with cuts all over their bodies, and a few even had to have their limbs amputated. Oddly enough, some people choose to keep piranhas in their home aquariums. However, piranhas can be tough to catch for this purpose because their sharp teeth can easily cut through fishing nets. Before buying one, be sure to check local laws as it is illegal to own them in many areas. Lawmakers often fear of the damage piranhas can cause to marine life if an owner decides to release them into a local stream.
3. When are piranhas most dangerous?
