[originaltext] An environment that is biologically diverse has lots of diffe

An environment that is biologically diverse has lots of different plants and animals. This is needed for people to have enough high-quality food to lead active and healthy lives.
    The idea of biodiversity recognizes that natural systems are complex and depend on one another.
    In agriculture, depending on only a few crops can be dangerous. One example is the Great Potato Famine in the eighteen forties. Ireland depended on potatoes as a food resource. But a disease ruined the crop for several years. More than one million people died from hunger.
    Yet experts say the world depends on only four crops to provide half its food energy from plants. These are wheat, maize, rice and potato. The experts say it is important to support a large number of different food crops and farm animals that can survive different conditions. Such diversity helps to reduce the risk from losing one main crop.
    Farmers also have a responsibility to protect wild species. The Food and Agriculture Organization says more than forty percent of all land is used for agriculture. Farm fields are an important place for wild animals to live and reproduce. Also, farmers must consider the effects that agriculture has on the environment. Farm pollution or poor agricultural methods can harm wetlands, rivers and other environments needed to support life.
    Invasive species are a severe threat to biodiversity. Plants and animals often spread without natural controls when they enter areas they are not native to. They can destroy crops, native species and property. Invasive species cost the world economy thousands of millions of dollars each year.
Q13: What does this report mainly talk about?
Ql4: According to experts, what are the four crops the world chiefly depends on?
Q15: Why are invasive species a severe threat to biodiversity?