如图所示,在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场,一个不计重力

题型:选择题

问题:

如图所示,在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场,一个不计重力的带电粒子从坐标原点O处以速度v进入磁场,粒子进人磁场时的速度方向垂直于磁场且与x轴正方向成120°角,若粒子穿过y轴正半轴后在磁场中到x轴的最大距离为a,则该粒子的比荷和所带电荷的正负是(  )

A.,正电荷

B.,正电荷

C.,负电荷

D.,负电荷

考点:带电粒子在匀强磁场中的运动
题型:选择题

动物是多种多样的,目前已知的大约有150万种.一类是脊椎动物动物,另一类是 无脊椎动物.这样分类的依据是______.

题型:选择题

世界遗产是指被联合国教科文组织和世界遗产委员会确认的人类罕见的、目前无法替代的财富,是全人类公认的具有突出意义和普遍价值的文物古迹及自然景观,包括文化遗产、自然遗产、文化与自然双重遗产和()四类。

A.文物

B.建筑群

C.遗址

D.文化景观

题型:选择题

设有员工实体Employee(employeeID,name,sex,age,tel,department),其中employeeID为员工号,name为员工姓名,sex为员工性别,age为员工年龄,tel为员工电话(要求记录该员工的手机号码和办公室电话),departID为员工所在部门号(要求参照另一部门实体Department的主码departID)。
Employee实体中存在的派生属性及其原因是 (58) :对Employee实体中属性departmentID的约束是 (59)

A.Primary Key NOTNULL

B.Primary Key

C.Foreign Key

D.Candidate Key

题型:选择题

某报纸曾刊登了这样一则消息:“那时,六大公司统治着德国化学工业市场,它们组成两大集团……此后不久,它又吞并了两大独立的公司。”从生产关系的角度来看,这段材料所反映的本质问题是()

A.化学工业发展迅速

B.工业生产竞争日趋激烈

C.垄断组织形成并不断扩大

D.工厂的规模不断扩火

题型:选择题

After the terrorist attacks in America last September, terrorist risk became the pariah of perils. The airline industry was most directly affected by the attacks, and it was the first to find that no one wanted to insure terrorist risk. Insurance companies immediately increased premiums and cut cover for airlines’ third-party terror and war liabilities to $ 50m per airline, per "event". Under pressure from airlines, the American government and the members of the European Union agreed to become insurers of last resort for airlines’ war and terrorist liabilities, for a limited period. These government guarantees are due to expire at the end of the month.

The American government has already agreed to extend its guarantee for another 60 days. The EU’s transport ministers are meeting next week in Brussels to decide what to do. Insurers and reinsurers are keen for the commercial market to resume the provision of all airline insurance as soon as possible. No wonder: The premiums for such cover have inevitably increased considerably.

However, in the case of terrorism, and especially of terrorism in the skies, a number of special factors arise. Some are purely practical: a disaster as sudden and unforeseen as the attacks on the World Trade Center has had destructive effects on the insurance industry. The maximum cover for third-party terrorist risk available in the primary aviation market is now $ 50m, and that is not nearly enough cover risks that are perceived to be much higher since September 11th. Even if the market could offer sufficient cover, another catastrophe on such a scale would be more than the market could cope with.

In addition, a rare and devastating risk of a political nature is arguably one that it is right for governments to cover, at least in part. In the wake of attacks by Irish terrorists the British government has recognized this point by agreeing to back a mutual fund to cover risks to property from terrorist attack.

In the case of the airlines, the appropriate answer is some form of mutual scheme with government backing. In fact, under the code-name "Equitime", representatives of airlines, insurers and the American government are setting up an insurance vehicle to be financed by airlines and reinsured by the government. Governments would guarantee the fund’s excess. risk, but their role would diminish as the fund grew.

Setting something up will take time. So, to bridge the gap, governments will have to remain insurer of last resort for airlines’ war and terrorist risk for some time to come.

By "terrorist risk became the pariah of perils" (Paragraph 1), the author means()

A. insurance companies increased premiums

B. airlines seek to avoid legal liabilities

C. terrorist attacks left insurers panicked

D. terrorist risk is unlikely to be insured

更多题库