用万用表电阻档来判断小功率二极管极性时，应选用（）档。A、R31 B、R310 C、R3

拟诊肾细胞癌患者出现一侧肾盂不显影可能为（）

A.肾盂及肾盏阻塞

B.肿瘤侵及肾盂

C.血块阻塞集合系统

D.肾静脉受累及

E.肾自截

Questions 21 to 25 are based on the following passage.

Lead deposits, which accumulated in soil and snow during the 1960’s and 70’s, were primarily the result of leaded gasoline emissions originating in the United States. In the twenty years that the Clean Air Act has mandated unleaded gas use in the United States, the lead accumulation worldwide has decreased significantly.

A study published recently in the journal Nature shows that air-borne leaded gas emissions from the United States were the leading contributor to the high concentration of lead in the snow in Greenland. The new study is a result of the continued research led by Dr. Charles Boutron, an expert on the impact of heavy metals on the environment at the National Center for Scientific Research in France. A study by Dr. Boutron published in 1991 showed that lead levels in arctic (北极的) snow were declining.

In his new study, Dr. Boutron found the ratios of the different forms of lead in the leaded gasoline used in the United States were different from the ratios of European, Asian and Canadian gasolines and thus enabled scientists to differentiate (区分) the lead sources. The dominant lead ratio found in Greenland snow matched that found in gasoline from the United States.

In a study published in the journal Ambio, scientists found that lead levels in soil in the Northeastern United States had decreased markedly since the introduction of unleaded gasoline.

Many scientists had believed that the lead would stay in soil and snow for a longer period.

The authors of the Ambio study examined samples of the upper layers of soil taken from the same sites of 30 forest floors in New England, New York and Pennsylvania in 1980 and in 1990. The forest environment processed and redistributed the lead faster than the scientists had expected.

Scientists say both studies demonstrate that certain parts of the ecosystem (生态系统) respond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute.

It can be inferred from the last paragraph that scientists （）

A.are puzzled by the mystery of forest pollution

B.feel relieved by the use of unleaded gasoline

C.still consider lead pollution a problem

D.lack sufficient means to combat lead pollution

第二届“挑战杯”中国大学生创业计划竞赛在哪里成功举办？（）

A.清华大学

B.浙江大学

C.上海交通大学

D.山东大学

某进出口公司委派采购员刘某到某棉区采购棉花，签发支票一张，其金额和收款人授权刘某根据棉区采购的实际情况填写，但明确告知支票的金额最多可以填写30万元，否则将超出公司目前在银行的存款额。支票的用途栏写明“采购棉花”。该公司并给刘某出具了明确的法定代表人授权委托书和公司营业执照副本。然而，刘某听信个体户叶某之言，企图利用短短的时间差，先做一笔彩电批发生意，赚取相当利润后再赴棉区采购棉花，于是，该二人将支票金额填写为183万元，收款人栏写上叶某的商号，再由叶某以商号名义背书给“某五金交电批发公司”。所购买的彩电转手成功后，全部款项被刘某和叶某卷逃。当“某五金交电公司”将叶某提交的支票送银行结算时，因某进出口公司账户上存款额不足而被退票。
问：

刘某与叶某应当承担何责任为什么

某汽车运输企业2008年车辆营运总里程为120万公里，同期发生行车责任事故8起，其中小事故5起、一般事故2起、大事故1起，该企业安全行车间隔里程为( )万公里。

A．15
B．20
C．24
D．40