题目

化学肥料对粮食增产起着重要作用，下列能作磷肥的是（ ） A．NH4HCO3B．CO（NH2）2C．KNO3D．Ca（H2PO4）2 答案：【考点】常见化肥的种类和作用． 【专题】常见的盐 化学肥料． 【分析】含有氮元素的肥料称为氮肥，含有磷元素的肥料称为磷肥，含有钾元素的肥料称为钾肥，同时含有氮、磷、钾三种元素中的两种或两种以上的肥料称为复合肥． 【解答】解：A、NH4HCO3中含有氮元素，属于氮肥，故选项错误． B、CIt is easy for us to tell our friends from our enemies. But can other animals do the same? Elephants can! They can use their sense of vision and smell to tell the difference between people who pose a threat and those who do not. In Kenya, researchers found that elephants react differently to clothing worn by men of the Maasai and Kamba ethnic groups. Young Maasai men spear animals and thus pose a threat to elephants; Kamba men are mainly farmers and are not a danger to elephants. In an experiment conducted by animal scientists, elephants were first presented with clean clothing or clothing that had been worn for five days by either a Maasai or a Kamba man. When the elephants detected the smell of clothing worn by a Maasai man, they moved away from the smell faster and took longer to relax than when they detected the smells of either clothing worn by Kamba men or clothing that had not been worn at all. Garment color also plays a role, though in a different way. In the same study, when the elephants saw red clothing not worn before, they reacted angrily, as red is typically worn by Maasai men. Rather than running away as they did with the smell, the elephants acted aggressively toward the red clothing. The researchers believe that the elephants’ emotional reactions are due to their different interpretations of the smells and the sights. Smelling a potential danger means that a threat is nearby and the best thing to do is run away and hide. Seeing a potential threat without its smell means that risk is low. Therefore, instead of showing fear and running away, the elephants express their anger and become aggressive. 71. According to the passage, which of the following statements is true about Kamba and Maasai people? A. Maasai people are a threat to elephants.   B. Kamba people raise elephants for farming. C. Both Kamba and Maasai people are elephant hunters. D. Both Kamba and Maasai people traditionally wear red clothing. 72. How did the elephants react to smell in the study? A. They attacked a man with the smell of new clothing. B. They needed time to relax when smelling something unfamiliar. C. They became anxious when they smelled Kamba-scented clothing. D. They were frightened and ran away when they smelled their enemies. 73. What is the main idea of this passage? A. Elephants use sight and smell to detect danger. B. Elephants attack people who wear red clothing. C. Scientists are now able to control elephants’ emotions.  D. Some Kenyan tribes understand elephants’ emotions very well. 74. What can be inferred about the elephant’s behavior from this passage? A. Elephants learn from their experiences. B. Elephants have sharper sense of smell than sight. C. Elephants are more intelligent than other animals. D. Elephants tend to attack rather than escape when in danger.