For 40 years, people in London have been happy to see parakeets   in their parks. The shocking green body and long tail have brought a bright color to the parks, which have attracted a lot of people. However, the parakeets are no longer welcome. They will push out local birds from trees to build their own nests, and will also take most of the food in the parks, such as seeds, fruit and nuts. Sometimes by accident, plants and animals are carried to new places. They are transported by trains, ships or even planes. Often, animals like fishes get transported in the water containers of ships. When these ships reach new places and pump out the water from their tanks, these animals will start a new life in a new place. Sometimes people take plants and animals from one part of the world to the other to solve a problem. But it will create a bigger problem. Years ago, the farmers of northern Australia brought the toads   from South America to their farms. They thought they would kill the beetles that harm the sugarcane crops. But the toad has done much more. It is now killing Australia's native animals, such as snakes, water birds and so on. People get interested in parakeets mainly because of   _  .
their appearance their singing their behavior their living environment