同一原件或线路的两套及以上主保护禁止（），至少保留一套主保护在投入状态

企业经营的政治环境包括( )。

A．政治的稳定性

B．国家物流发展规划

C．国际关系

D．法制体系

E．国家政治体制

经济合同的主要条款有（）

A、标的

B、数量和质量

C、价款或酬金

D、履行的期限、地点和方式

E、违约责任

在数据表视图下向表中输入数据，在末输入数值之前，系统自动提供的数值字段的属性是 【8】 。

A new study finds that blacks on death row (1) of killing whites are more likely to be executed than whites who kill minorities. It also concludes that blacks who kill (2) minorities are (3) likely to be executed than blacks who kill whites. For example, there is more than a twofold greater risk that an African-American who killed a white will be executed than a white person who kills a (4) victim. A Hispanic is at least 1.4 (5) more likely to be executed (6) such an offender kills a white.

The researchers of the study believe that there are two (7) explanations.. First, prosecutors often win (8) office if they win well-publicized cases. When a black kills a white, such killings gets more (9) and this idea can be (10) by many famous cases. (11) , the court judges at the state level are often (12) to elections, called retention elections. Retention election or judicial retention within the United States court system, is a periodic process, in which the voter (13) approval or disapproval for the judges presently (14) their position, and a judge can be removed from the position if the (15) of the citizens vote him or her out. Just as the researchers (16) out, death penalty is (17) political.

The findings of the study, in short, show that American justice systems clearly (18) white lives more than those of blacks or Hispanics. The researchers also say their findings (19) serious doubts about (20) that the U.S. criminal justice system is colorblind.

9（）

A.attendance

B.attraction

C.tempt

D.publicity

什么是金属材料的疲劳与疲劳极限？