单选题设A为n阶矩阵，则在下列条件中，不是“A的特征值为-1”的充分条件的是

单选题设连续函数f(x)满足f(2x)=2f(x)，则，其中a为

单选题周长相同的圆、正方形和正三角形的面积分别为a，b和c，则a，b，c的大小关系是( )． (A) a＞b＞c (B) b＞c＞a (C) c＞a＞b (D) a＞c＞b (E) A、B、C、D都不正确

单选题[2014年1月]已知直线l是x2+y2=5在点(1，2)的切线，则l在y轴上的截距是()。

单选题在命题①设收敛，则收敛．②设收敛且n→∞时an与bn是等价无穷小，则收敛．③设收敛，则．④设收敛，又绝对收敛，则绝对收敛．中正确的是A.①．B.②．C.③．D.④．

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．(A)8(B)6(C)4(D)7(E)10

单选题若级数收敛，则级数A．收敛．B．收敛．C．收敛．D．收敛．

单选题甲容器中有8%的食盐水300g，乙容器中有12.5%的食盐水120g．往甲、乙两个容器分别倒入等量的水，使两个容器的食盐水浓度一样．则例倒入( )g水．

单选题已知动点P在边长为2的正方形ABCD的边上沿着A→B→C→D运动，x表示点P由点A出发所经过的路程，y表示△APD的面积，则y与x函数关系的图像大致为()。(E)以上答案均不正确

单选题 Passage 5 Darkness approached and a cold, angry wind gnawed at the tent like a mad dog. Camped above treeline in the Wind River Mountains of Wyoming, the torrents of air were not unexpected and only a minor disturbance compared to the bestial gnawing going on behind my belly button. In an attempt to limit exposure of my bare bottom to the ice-toothed storm, I had pre-dug a half dozen catholes within dashing distance. Over and over, through the long night, the same scenario was repeated: out of the bag, out of the tent, rush, squat, rush back. "Everyone can master a grief," wrote Shakespeare, "but he that has it." Diarrhea, the modern word, resembles the old Greek expression for "a flowing through." Ancient Egyptian doctors left descriptions of the suffering of Pharaohs scratched on papyrus even before Hippocrates, the old Greek, gave it a name few people can spell correctly. An equal opportunity affliction, diarrhea has laid low kings and common men, women, and children for at least as long as historians have recorded such fascinating trivia. It wiped out, almost, more soldiers in America's Civil War than guns and swords. In the developing world today, acute diarrhea strikes more than one billion humans every year, and leaves more than five million dead, usually the very young. Diarrhea remains one of the two most common medical complaints of humanity. "Frequent passage of unformed watery bowel movements," as described by Taber's Cyclopedic Medical Dictionary, diarrhea falls into two broad types: invasive and non-invasive. From bacterial sources, invasive diarrhea, sometimes called "dysentery," attacks the lower intestinal wall causing inflammation, abscesses, and ulcers that may lead to mucus and blood (often "black blood" from the action of digestive juices) in the stools, high fever, "stomach" cramps from the depths of hell, and significant amounts of body fluid rushing from the patient's nether region. Serious debilitation, even death, can occur from the resulting dehydration and from the spread of the bacteria to other parts of the body. Non-invasive diarrhea grows from colonies of microscopic evil-doers that set up housekeeping on, but do not invade, intestinal walls. Toxins released by the colonies cause cramps, nausea, vomiting, and massive gushes of fluid from the patient's lower intestinal tract. Non-invasive diarrhea carries a high risk for dehydration.

单选题下列广义积分收敛的是______。A．B．C．D．

单选题设f(x)在(-∞，+∞)上可导，且对任意的x1和x2，当x1＞x2时都有f(x1)＞f(x2)，则______． A．对任意x，f'(x)＞0 B．对任意x，f'(-x)≤0 C．函数f(-x)单调增加 D．函数-f(-x)单调增加