题目

已知sinα是方程6x=1-的根，那么的值等于（    ）A.±         B.±             C.        D. 答案：解析：∵6x=1-,∴=或=-(舍去).∴x=.又∵sinα是方程6x=1-的根，∴sinα=.∴cosα=±.∴.答案：ATeens are more likely to behave badly if their parents expect them to，a new US study has found.“Parents who believe they are simply being realistic might actually be having a bad effect on their children，” Christy Buchanan，a teacher at Wake Forest University and one of the authors of the study，said. “Bad expectations on the part of both parents and children predict more rebellious (叛逆的) behaviors later on.”The finding came from a study of more than 250 sixth­ and seventh­graders and their mothers. They were examined at the start of the study and again one year later. If kids’ mothers expected them to take more risks and be more rebellious，higher chances of risky behavior were seen.This_was_also_true when kids had bad expectations of themselves.“Sometimes parents expect more negative behavior from their children than they should based on the children’s history of behavior，” Buchanan said.Parents shouldn’t be naive (无知的) about the possibility of bad behavior，she said，but it’s also a mistake to think that children who are well­behaved will naturally become rebellious at the age of 13.“By thinking risk­taking or rebelliousness is normal for teenagers and showing that to their children，parents might add to other messages from society that make teenagers feel that they are strange if they are not willing to take risks or break laws，” she said.“This can mean，for example，that when parents expect teens to drink before they turn 21 or to do other risky behaviors，kids are less likely to refuse to do so later in their lives.”On the other hand，parents’ expectations that teens can exhibit good behaviors and refuse to behave badly or to take risks could help reduce the possibility of bad behavior，Buchanan said.“As a parent，you should put expectations on your children carefully.”1.The passage is centered around the topic of________.A.parental rightsB.children’s habitsC.parental educationD.parent­children relationship2.What do we know about the study?A.Only mothers were examined.B.Participants were examined twice.C.250 people were examined in the study.D.Christy Buchanan was the only author of the study.3.What does the underlined part “This was also true” in Paragraph 3 refer to?A.The kids were more likely to take dangerous behavior.B.The kids would have bad expectations of their parents.C.The kids were likely to go against their mothers.D.Mothers expected their kids to behave badly.4.Children may be more rebellious if________.A.they know parents think risk­taking is normalB.parents put little expectation on themC.they behave well before they turn 13D.they are asked not to take risks5.What might be the most suitable title for the passage?A.Risk­taking is normal for teens.B.Why are my teens behaving badly?C.Don’t expect too much from your teens.D.Bad expectations lead to bad­behaving teens.