单选题有n(n∈N)件不同的产品排在一排，若其中A、B两件产品排在一起的不同排法有48种，则n=( )．

单选题设，其中bn=2∫01f(x)sinnnxdx，则等于A．B．C．D．

单选题曲线y=x(x-1)(2-x)与X轴所围图形的面积可表示为()。A．B．C．D．

单选题若二次型为正定二次型，则λ的取值范围是______

单选题Self-esteem is the collection of beliefs or feelings we have about ourselves, our "self-perceptions. " How we define ourselves influences our motivations, attitudes, and behaviors and affects our emotional adjustment. Patterns of self-esteem start very early in life. For example, a toddler who reaches a milestone experiences a sense of accomplishment that bolsters self-esteem. Learning to roll over after dozens of unsuccessful attempts teaches a baby a "can-do" attitude. The concept of success following persistence starts early. As kids try, fail, try again, fail again, and then finally succeed, they develop ideas about their own capabilities. At the same time, they're creating a self-concept based on interactions with other people. This is why parental involvement is important to helping kids form accurate, healthy self-perceptions. Self-esteem fluctuates as kids grow. It's frequently changed and fine-tuned, because it is affected by a child's experiences and new perceptions. So it helps to be aware of the signs of both healthy and unhealthy self-esteem. Kids with low self-esteem may not want to try new things, and may frequently speak negatively about themselves. They tend to be overly critical of and easily disappointed in themselves. Kids with low self-esteem see temporary setbacks as permanent, intolerable conditions, and a sense of pessimism predominates. Kids with healthy self-esteem tend to enjoy interacting with others. They're comfortable in social settings and enjoy group activities as well as independent pursuits. When challenges arise, they can work toward finding solutions and voice discontent without belittling themselves or others. How can a parent help to foster healthy self-esteem in a child? Kids who don't feel safe or are abused at home will suffer immensely from low self-esteem. A child who is exposed to parents who fight and argue repeatedly may become depressed and withdrawn. Also watch for signs of abuse by others, problems in school, trouble with peers, and other factors that may affect kids' self-esteem. Deal with these issues sensitively but swiftly. And always remember to respect your kids. If you suspect your child has low self-esteem, consider doing something about it. Family and child counselors can work to uncover underlying issues that prevent a child from feeling good about him or herself. Therapy can help kids learn to view themselves and the world positively. When kids see themselves in a more realistic light, they can accept who they truly are. With a little help, every child can develop healthy self-esteem for a happier, more fulfilling life.

单选题设等差数列{an}的前n项和为Sn，且a3=10，S8＞0，S9＜0，则数列{an}的公差d的取值范围为______．A．(-∞，-5)B．C．D．(5，+∞)E．

单选题某同学参加体育考试，要求进行10次投篮，若该同学共投中5次，其中有4次连续命中，则该同学的投篮情况共有______种可能．

单选题设则使x+y+z=74成立的y值是()．

单选题某高速公路收费站对过往车辆收费标准是：大客车10元，小客车6元，小轿车3元。某日此站共收费4700元，则小轿车通过的数量为420辆。 (1)大、小客车之比是5:6，小客车与小轿车之比为4:7 (2)大、小客车之比是6:5，小客车与小轿车之比为7:4

单选题二重积分(D：x2+y2≤R2)的值______A.是0B.只有当m，n均为奇数时，才是0C.只有当m，n均为偶数时，才是0D.只要m，n中有一个为奇数时，就为0

单选题设3阶矩阵A有3个互不相同的特征值λ 1 ，λ 2 和λ 3 ，其对应的特征向量分别为ξ 1 ，ξ 2 和ξ 3 ．则向量组ξ 1 、A(ξ 1 +ξ 2 )、A 2 (ξ 1 +ξ 2 +ξ 3 )线性无关的充要条件是

单选题设X，Y是相互独立的随机变量，它们的分布函数分别是FX(x)，FY(y)，则Z=max(X，Y)的分布函数是______．