In the last 500 million years, there have been five mass extinction events on Earth. In the third event, 【小题1】 is known as the “Great Dying”, 90% to 96% of all species died out. Of course, species died out due to many 【小题2】 (cause). But nowadays, human activity has affected all types of species that we depend on for living. We need to take action 【小题3】 (avoid) the sixth mass extinction. We should take steps to save endangered animals and plants, and set up special areas to take care of them 【小题4】 the next extinction comes that may wipe out the entire species.