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In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
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Article: Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away or fight back. Plants certainly cannot run away, and they lack teeth and claws. But plants can defend themselves by using both physical and chemical means. Some plants have their own ways to keep animals away. For example, the leaves of the holly plant have sharp spines that discourage grass-eating animals. Holly leaves on lower branches have more spines than leaves on upper branches. This is because the lower leaves are easier for most animals to reach. Some plants, such as the oak tree, have thick and hard leaves that are difficult for animals to eat. Some grasses may contain a sandy material; eating such grasses wears down the animal's teeth. Many plants also have chemical defenses. Some plants produce chemicals that taste bitter or cause an unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a caterpillar bites a tobacco leaf, the leaf produces a chemical messenger. This messenger sends to the roots the information to produce more nicotine. The higher levels of nicotine discourage the caterpillar. Many plants depend on both physical and chemical defenses. A certain plant in China, for instance, has prickly leaves, and each prickle contains poisonous venom A single experience with this kind of plant will teach an animal to stay away from it in the future.
Answer: physical means
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To defend themselves, oak trees use _ .

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Article: Bob Butler lost his legs in a 1965 landmine explosion in Vietnam. He returned home as a war hero. Twenty years later,he proved once again that heroism comes from the heart. Butler was working in his garage in a small town in Arizona on a hot summer day when he heard a woman's screams coming from a nearby house. He rolled his wheelchair toward the house,but the dense bush wouldn't allow him to approach the back door. So he got out of his chair and crawled through the dirt and bushes. "I had to get there,"he says. "It didn't matter how much it hurt." When Butler arrived at the house,he traced the screams to the pool,where a three year old girl,Stephanie,was lying at the bottom. She had been born without arms and had fallen in the water and couldn't swim. Her mother stood over her baby screaming loudly. Butler dove to the bottom of the pool and brought little Stephanie up to the deck. Her face was blue,she had no pulse and she was not breathing. Butler immediately went to work performing CPR to revive her while Stephanie's mother telephoned the fire department. She was told the rescue team was already out on a call .Helplessly,she sobbed and hugged Butler's shoulders. As Butler continued with his CPR,he calmly reassured Stephanie's mother. "Don't worry,"he said. "I was her arms to get out of the pool. It'll be okay. I'm now her lungs. Together we can make it." Seconds later the little girl coughed,regained consciousness and began to cry. As they hugged and rejoiced together,the mother asked Butler how he knew it would be okay. "When my legs were blown off in the war,I was all alone in a field,"he told her." No one was there to help except a little Vietnamese girl. As she struggled to drag me into her village,she whispered in broken English,'It okay. You can live. I be your legs. Together we make it.'" "This was my chance,"he told Stephanie's mom,"to return the favor."
Answer: believed that everything will be OK and he would make it.
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When Butler heard the woman's scream, he _ .

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Article: Disposing of waste has been a problem since humans started producing it. As more and more people choose to live close together in cities,the waste disposal problem becomes increasingly difficult. During the eighteenth century,it was usual for several neighboring towns to get together to select a faraway spot as a dump site. People would transport household rubbish,rotted wood and old possessions to the site. Regularly some of the trash was burned and the rest was buried. The unpleasant sights and smells caused no problem because nobody lived close by. Factories and some other industrial sites also had waste to be disposed of. Those located on rivers often just poured the unwanted remains into the water. Others built huge burners with chimneys to deal with the problem. Several facts make these choices unacceptable to modern society. The first problem is space. Dumps , are most needed in heavily populated areas. Such areas rarely have empty land suitable. Farm areas are refusing to accept rubbish from elsewhere,cheap land in major city areas to dispose wastes is nonexistent . Awareness of pollution dangers has resulted in more strict rules of waste disposal. Pollution of rivers,ground water,land and air is a price people can no longer pay to get rid of waste. The amount of waste,however, continues to grow. Recycling efforts have become commonplace,and many towns require their people to take part. Even the most efficient recycling programs,however,can hope to deal with only about 50 percent of a city's reusable waste,so more people should be involved in recycling programs.
Answer: Waste Disposal Problem
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The most suitable title for this passage would be _ .