干砌石护坡鼓肚凹腰时，其维修内容包括（）。A.拆除缺陷部位 B.平顺内部石料 C.干

队列研究证明高胆固醇血症是冠心病的危险因素(RR=3，P<0.05)。但进行以医院为基础的病例对照研究时，发现病例组与对照组的血清胆固醇水平没有显著性差异(0R=1.1，P>0．05)。进一步分析显示，这种病例对照研究与队列研究结果之问的差异，是因为冠心病患者在诊断为冠心病后大多改变了其饮食习惯和生活习惯，从而使患者的血清胆固醇下降了。这属于下列哪一种偏倚

A．检出偏倚

B．易感性偏倚

C．Neyman偏倚

D．Berkson’s偏倚

E．诊断怀疑偏倚

阅读理解。

     If you were to walk up to Arthur Bonner and say, "Hey, Butterfly Man," his face would break into a

smile. The title suits him, And he loves it.

     Arthur Bonner works with the Palos Verdes blue butterfly, once thought to have died out. Today the

butterfly is coming back thanks to him. But years ago if you'd told him this was what he'd be doing someday,

he would have laughed, "You're crazy." As a boy, he used to be "a little tough guy on the streets". At age

thirteen he was caught by police stealing. At eighteen, he landed in prison for shooting a man.

     "I knew it had hurt my mom," Bonner said after he got out of prison. "So I told myself I would not put

my room through that pain again."

     One day he met Professor Mattoni, who was working to rebuild the habitat for an endangered butterfly

called El Segundo blue.

     "I saw the sign 'Butterfly Habitat' and asked, 'How can you have a habitat when the butterflies can just

fly away?'" Bonner recalls. "Dr. Mattoni laughed and handed me a magnifying glass (放大镜), 'Look at the

leaves.' I could see all these caterpillars (蝴蝶的幼虫) on the plant. Dr Mattoni explained, 'Without the plant,

there are no butterflies.'"

     Weeks later, Bonner received a call from Dr. Mattoni who told him there was a butterfly that needed help.

That was how he met the Palos Verdes blue. Since then he's been working for four years to help bring the

butterfly back. He grows astragals, the only plant the butterfly eats. He collects butterflies and brings them

into a lab to lay eggs. Then he puts new butterflies into the habitat.

     The butterfly's population once almost zero, is now up to 900. For their work, Bonner and Dr. Mattoni

received lots of awards. But for Bonner, he earned something more: he turned his life around.

     For six years now Bonner has kept his promise to stay out of prison. While he' s bringing back the Palos

Verdes blue, the butterfly has helped bring him back, too.

1. When he was young, Arthur Bonner _____.

A. broke the law and ended up in prison

B. was fond of shooting and hurt his morn

C. often offered necessary help to other people

D. often caught butterflies and took them home

2. Bonner came to know the Palos Verdes blue after he _____.

A. found the butterfly had died out

B. won many prizes from his professor

C. met Dr. Mattoni, a professor

D. collected butterflies and put them into a lab

3. From the last sentence of the text, we learn that raising butterflies has _____.

A. made Bonner famous

B. changed Bonner's life

C. brought Bonner wealth

D. enriched Bonner's knowledge

4. Which of the following would be the best title for the text?

A. A Promise to Morn

B. A Man Saved by Butterflies

C. A Story of Butterflies

D. A Job Offered by Dr. Mattoni

对放喷管线应每隔30m打水泥基墩，用“U”形卡子固定牢靠。

某内部审计师对销售发票系统的准确性感兴趣。单张发票货币金额变动较大，内部审计师有合理的原因相信发票处理过程中的错误率在3%到10%之间，但不能确定错误的金额大小。在确定选用哪一种特定的变量抽样技术时，审计人员必须意识到（）

A.由于错误金额无法确定，分层均值估计在这种情况下作用较小

B.在3%到10%的错误率范围，对总体进行分层无益的

C.在这种情况下，差异估计或比率估计都比不分层的均值抽样估计要有效

D.除非总体每一项目都有审计值与帐面值，否则差异估计或比率估计都是不可行的

某电路输出信号功率是输入信号功率的1/5，该电路的增益约为（）

A.-7dB

B.3.5dB

C.-5dB

D.-14dB