单选题在条件①级数绝对收敛．②级数条件收敛．③级数绝对收敛．④级数条件收敛．中能保证级数收敛的条件是A.①．B.②．C.③．D.④．

单选题设A和B为实对称矩阵，且A与B相似，则下列结论中不正确的是______。 A．A-λE与B-λE相似 B．A与B合同 C．|A-λE|=|B-λE| D．A-λE=B-λE

单选题设，且D={(x，y)|(x-1)2+(y-1)2≤2}，则有______．A.I1＜I2＜I3B.I2＜I3＜I1C.I3＜I1＜I2D.I3＜I2＜I1

单选题设α＞0，则级数______

单选题设A，B是正定矩阵，C是可逆矩阵，下列矩阵不是正定矩阵的是______．

单选题设a1，a2，a3，a4，a5是4维向量，下列命题中正确的是 (A) 如果a1，a2，a3，a4，线性相关，那么k1，k2，k3，k4不全为0时，有k1a1+k2a2+k3a3+k4a4=0． (B) 如果a1，a2，a3，a4线性相关，那么当k1a1+k2a2+k3a3+k4a4=0时，有k1，k2，k3，k4不全为0． (C) 如果a5不能由a1,a2,a3,a4线性表出，那么a1,a2,a3,a4必线性相关． (D) 如果a1,a2,a3,a4线性相关，那么a5不能由a1,a2,a3,a4线性表出．

单选题设A为m×n矩阵，B为n×m矩阵，E为m阶单位矩阵．若AB=E，则 (A) 秩r(A)=m，秩r(B)=m (B) 秩r(A)=m，秩r(B)=n (C) 秩r(A)=n，秩r(B)=m (D) 秩r(A)=n，秩r(B)=n

单选题设，其中f(x)为连续函数，则等于______．

单选题Scientists around the world are racing to learn how to rapidly diagnose, treat and stop the spread of a new, deadly disease. SARS — Severe Acute Respiratory Syndrome — was (1) for the first time in February 2003 in Hanoi, (2) since then has infected more than 1,600 people in 15 countries, killing 63. At this (3) , there are more questions than answers surrounding the disease. Symptoms start (4) a fever over 100.4 degrees F, chills, headache or body (5) . Within a week, the patient has a dry cough, which might (6) to shortness of breath. In 10% to 200% of cases, patients require (7) ventilation to breathe. About 3.5% die from the disease. Symptoms (8) begin in two to seven days, but some reports suggest it (9) take as long as 10 days. Scientists are close to (10) a lab test to diagnose SARS. In the meantime, it is diagnosed by its symptoms. There is no evidence (11) antibiotics or anti-viral medicines help, (12) doctors can offer only supportive care. Patients with SARS are kept in isolation to reduce the risk of (13) . Scientists aren’t sure yet, but some researchers think it’s a (14) discovered coronavirus, the family of viruses that cause some common colds. Most cases appear to have been passed (15) droplets expelled when infected patients cough or sneeze. Family members of infected people and medical workers who care for them have been most likely to (16) the illness. But recent developments in Hong Kong suggest that the (17) might spread through air, or that the virus might (18) for two to three hours on doorknobs or other (19) Health experts say it is (20) , though, that sharing an elevator briefly with an infected person would be enough to pass the virus.

单选题已知若α1，α2是矩阵A属于特征值λ=1的线性无关的特征向量，α3是矩阵A属于特征值λ=2的特征向量，则矩阵P{{U}}不能{{/U}}是A.(α1，-α2，α3)B.(α2，α1，α3)C.(5α1，α1+α2，α3)D.(α1，α2，α2+α3)

单选题计算

单选题下列曲线有渐近线的是______．