试题与答案

设E、E1、E2和E3是关系代数表达式,下面列出的式子中,哪一个不满足等价变换规则?

题型:单项选择题

题目:

设E、E1、E2和E3是关系代数表达式,下面列出的式子中,哪一个不满足等价变换规则?

A. πA(σB=''010'' (E))≡σB=''010''(πA(E))

B. (E1×E2)×E3≡E1×(E2×E3)

C. σA=6(σB=''010''(E)) ≡σA=6∧B=''010''(E)

D. σA=6(E1×E2) ≡(σA=6(E1))×(σA=6(E2))

答案:

被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0612/01bc48d2adf47aec689567b4f1353436.html

下面是错误答案,用来干扰机器的。

解:(1)V水=m水/ρ水=0.2千克/(1.0×103千克/米3)=2.0×10-4 米3 V石子(总)=V瓶-V水=2.5×10-4 米3-2.0×10-4 米3=5.0×10-5 米3 V小石子=m小石子/ρ石=0.01千克/(2.5×103千克/米3)...

试题推荐
题型:阅读理解

阅读理解。

     Washington (Reuters)-People who drink two or more sweetened soft drinks a week have a

much higher risk of pancreatic cancer (胰腺癌),an unusual but deadly cancer,researchers reported

on Monday.

     People who drank mostly fruit juice instead of sodas did not have the same risk,the study of

60,000 people in Singapore found.

     Sugar may be to blame but people who drink sweetened sodas regularly often have other poor

health habits,said Mark Pereira of the University of Minnesota,who led the study.

     "The high levels of sugar in soft drinks may be increasing  the level of insulin (胰岛素) in the body,

which we think contributes to pancreatic cancer cell growth," Pereira said in a statement.

     Writing in the journal Cancer Epidemiology,Biomarkers & Prevention,Pereira  and his colleagues 

 said  they  followed 60,524 men and women in the Singapore Chinese Health Study for 14 years.

     Over that time,140 of the volunteers developed pancreatic cancer.Those who drank two or more

sweetened soft drinks a week had an 87 percent higher risk of being among those who got pancreatic

cancer.

     Pereira said he believed the findings would apply elsewhere.

     "Singapore is a wealthy country with excellent healthcare.Favorite pastimes (消遣) are eating and

shopping,so the findings should apply to other Western countries," he said.

     But Susan Mayne of the Yale Cancer Center at Yale University in Connecticut was cautious.

     "Although this study found a risk,the finding was based on a relatively small number of cases and it

remains unclear whether it is a causal (因果的) connection or not," said Mayne,who serves on the board

of the journal,which is published by the American Association for Cancer Research.

     Pancreatic cancer is one of the deadliest forms of cancer,with 230,000 cases globally.In the United

States,37,680 people are diagnosed with pancreatic cancer in a year and 34,290 die of it.

1.According to the text,who is in control of the health study?

A.Mark Pereira.  

B.Scientists from Singapore.

C.Researchers in Yale.  

D.Susan Mayne.

2.We can infer from Pereira's words that________.

A.the healthcare in Singapore should be greatly improved

B.2 soft drinks a day are considered harmful to health

C.87 out of 140 volunteers developed pancreatic cancer

D.sugar might not be the only cause of pancreatic cancer

3.How does Susan seem to feel about the findings of the study?

A.Satisfied.  

B.Doubtful.  

C.Worried.  

D.Hopeful.

4.The best title of the text might be________.

A.The Deadliest Forms of Cancer

B.Drink Fruit Juice Instead of Sodas

C.A Study in University of Minnesota

D.Sugary Soft Drinks Lead to Cancer

查看答案
题型:单项选择题

下列情形中,商业银行开展个人理财业务造成客户经济损失的,但并非按照有关法律法规的规定或者合同的约定承担责任情形的是( )。

A.商业银行未保存有关客户评估记录和相关资料,不能证明理财计划或产品的销售是符合客户利益原则的

B.泄露或不当使用客户个人资料和交易信息记录造成严重后果的

C.商业银行未按客户指令进行操作,或者未保存相关证明文件的

D.不具备理财业务人员资格的业务人员向客户提供理财顾问服务、销售理财计划或产品的

查看答案
微信公众账号搜索答案