单选题方程y"-3y'+2y=xe2x的待定特解y*应取( )．

单选题 The question of whether war is inevitable is one which has concerned many of the world's great writers. Before considering this question, it will be useful to introduce some related concepts. Conflict, defined as opposition among social entities (实体) directed against one another, is distinguished from competition, defined as opposition among social entities independently striving for something which is in inadequate supply. Competitors may not be aware of one another, while the parties to a conflict are. Conflict and competition are both categories of opposition, which has been defined as a process by which soical entities function in the disservice of one another. Opposition is thus contrasted with cooperation, the process by which social entities function in the disservice of one another. These definitions are necessary because it is important to emphasize that competition between individuals or groups is inevitable in a world of limited resources, but conflict is not. Conflict, nevertheless, is very likely to occur, and is probably an essential and desirable element of human societies. Many authors have argued for the inevitability of war from the premise that in the struggle for existence among animal species, only the fittest survive. In general, however, this struggle in nature is competition, not conflict. Social animals, such as monkeys and cattle, fight to win or maintain leadership of the group. The struggle for existence occurs not in such fights, but in the competition for limited feeding areas and for the occupancy of areas free from meat eating animals. Those who fail in this competition starve to death or become victims to other species. This struggle for existence does not resemble human war, but rather the competition of individuals for jobs, markets, and materials. The essence of the struggle is the competition for the necessities of life that are insufficient to satisfy all. Among nations there is competition in developing resources, trades, skills, and a satisfactory way of life. The successful nations grow and prosper, the unsuccessful decline. While it is true that this competition may include efforts to expand territory at the expense of others, and thus lead to conflict, it cannot be said that, war-like conflict among nations is inevitable, although competition is.

单选题已知关于x的方程x 2 一6x+(a一2)∣x一3∣+9—2a=0有两个不同的实数根，则系数a的取值范围是( )．

单选题两相似三角形△ABC与△A"B"C"的对应中线之比为3：2，若S △ABC =a+3，S △A"B"C" =a-3则a=( )。

单选题在△ABC中，若c-a等于AC边上的高h，则等于______。A．-1B．C．D．1

单选题已知，，，则______．

单选题设an＞0，n=1，2，3，…，若发散，收敛，则下列结论正确的是

单选题不同的5种商品在货架上排成一排，其中甲、乙两种必须排在一起，丙、丁两种不能排在一起，则不同的排法共有______

单选题某操场上有学生100人，其中男生占，后来又来了若干名男生，使得男生占女生人数的，则后来又来了()名男生．

单选题今年父亲的年龄是儿子年龄的10倍，6年后父亲的年龄是儿子年龄的4倍，那么2年前，父亲比儿子大______ A.25岁 B.26岁 C.27岁 D.28岁 E.29岁