单选题如图7-2，AB是半圆的直径，O是圆心，AB=12，从AB延长线上一点P作的切线，与切于D，DE⊥AB于E，若AE:EB=3:1，则图中阴影部分面积为( )．

单选题已知不等式ax2+bx+2＞0的解集是，则a的值为______

单选题某单位职工在调出15名女职工后，男女职工比例为2:1，若再调出45名男职工后，男女职工比例变为1:5，则原有男职工______人． A．66 B．60 C．56 D．50

单选题设A为n阶矩阵，且满足等式A2=A，E为n阶单位矩阵，则下列结论正确的是

单选题设A为n阶方阵，r(A)=n-3，且a1、a2、a3是Ax=0的三个线性无关的解向量，则Ax=0的基础解系为()。

单选题甲商店销售某种商品，该商品的进价为每件90元，若每件定价为100元，则一天内能销售500件，在此基础上，定价每增加1元，一天便少售出10件，甲商店欲获得最大利润，则该商品的定价为______

单选题已知a，b，c为非零向量，且a·b=0，b×c=0，则______

单选题若f(x)为[a，b]上的连续函数，则()A．小于0B．大于0C．等于0D．不确定

单选题设n维列向量，矩阵A=E-4ααT，其中E是n阶单位矩阵，若n维列向量β=(1，1，…，1)T，则向量Aβ的长度为A．B．C．n.D．n2.

单选题{{B}}Directions:{{/B}} There are 5 reading passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C, and D. You should decide on the best choice and mark your answer on the ANSWER SHEET by blackening the corresponding letter in the brackets. In the United States, 36 states currently allow capital punishment for serious crimes such as murder. Americans have always argued about the death penalty. Today, there is a serious question about this issue: Should there be a minimum age limit for executing criminals? In other words, is it right for convicted murderers who kill when they are minors--i, e. , under the age of 18--to receive the death penalty? In most other countries of the world, there is no capital punishment for minors. In the United States, though, each state makes its own decision. Of the 36 states that allow the death penalty, 30 permit the execution of minors. In the state of South Carolina, a convicted murderer was given the death penalty for a crime he committed while he was a minor. In 1977, when he was 17 years old, James Terry Roach and two friends brutally murdered three people. Roach's lawyer fought the decision to execute him. The young murderer remained on Death Row (a separate part of prison for convicted criminals who are sentenced to death) for ten years while his lawyer appealed to the governor. The lawyer argued that it is wrong to execute a person for a crime he committed while he was a minor. In the United States, the governor of a state has the power to change a sentence from the death penalty to life in prison. Nonetheless, the governor of South Carolina refused to stop the execution. Roach was finally executed by electrocution in 1986. This is not the first time a criminal was executed in South Carolina for a crime he committed when he was a minor. In 1944, a 14-year-old boy died in that state's electric chair. In Indiana, a 16-year-old girl was on Death Row for a crime she committed when she was 15. Paula Cooper and three friends stabbed an elderly woman to death in 1986. They robbed the old woman to get money to play video games. At the time of the murder, the minimum age limit for executions in that state was 10. Cooper's lawyer appealed to the governor of Indiana to stop the execution because the convicted killer was very young and because she was abused in childhood. The Indiana governor, who favors the death penalty, said that he had to let the courts do their job.