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在平面直角坐标系xOy内，曲线y=x3-3x2+1在点(1，-1)处的切线方程为（）．
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Questions 47 to 51 are based on the following passage. Child maltreatment (虐待) is a global problem with serious life-long consequences. There are no reliable global estimates for the common existing of child maltreatment. Data for many countries, especially low- and middle-income countries, are lacking. Child maltreatment is complex and difficult to study. Current estimates vary widely depending on the country and the method of research used. Nonetheless, international studies reveal that approximately 20% of women and 5-10% of men report being sexually abused as children, while 25-50% of all children report being physically abused. Additionally, many children are subject to emotional abuse (sometimes referred to as psychological abuse) and to neglect. Every year, there are an estimated 31,000 homicide (他杀) deaths in children under 15. This number underestimates the true extent of the problem, as a significant proportion of deaths due to child maltreatment are incorrectly attributed to falls, bums and drowning and other causes. Child maltreatment causes suffering to children and families and can have long-term consequences. Maltreatment causes stress that is associated with disruption in early brain development. Extreme stress can impair the development of the nervous and immune systems. Consequently, as adults, maltreated children are at increased risk for behavioral, physical and mental health problems such as depression, smoking, unintended pregnancy, alcohol and drug misuse, etc. Via the behavioral and mental health consequences, maltreatment can contribute to heart disease, cancer, suicide and sexually transmitted infections. Beyond the health consequences of child maltreatment, there is an economic impact, including costs of hospitalization, mental health treatment, child welfare, and longer-term health costs. A number of risk factors for child maltreatment have been identified. These risk factors are not present in all social and cultural contexts, but provide an overview when attempting to understand the causes of child maltreatment. It is important to emphasize that children are the victims and are never to blame for maltreatment. A number of characteristics of an individual child may increase the likelihood of being maltreated: being either under four years old or an adolescent; being unwanted, or failing to fulfill the exceptions of parents; and having special needs, crying persistently or having abnormal physical features. According to international studies, more than one fourth of all children said they had been ______.
Directions: In this section, you will hear 8 short conversations and 2 long conversations. At the end of each conversation, one or more questions will be asked about what was said. Both the conversation and questions will be spoken only once. After each question there will be a pause. During the pause, you must read the four choices marked, and decide which is the best answer. Then mark the corresponding letter on Answer Sheet 2 with a single line through the centre.
常形成鹿角型结石的是
Questions 23 to 25 are based on the conversation you have just heard.
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