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Frogs are an environmental warning system. They have skin which takes in whatever is in the environment. This means that if the environment is （1） , a frog’s skin takes in the pollution and the frog dies. For this reason, if there’s something wrong in the environment, frogs are the first to die. If there are （2） frogs, it’s a good sign that the environment is healthy.

Frog numbers around the world have been dropping at a faster （3） in recent years than ever before. Up to 200 kinds of frogs have died out （4） 1980. This is a disaster. Frogs are needed in the food chain as food for animals like snakes, birds and fish. Frogs are also needed in the food chain to eat insects （5） grasshoppers. The world needs frogs.