下列由左到右的变形，属于因式分解的是（ ） A．（2x-3）（2x+3）=4x2

SUPCONJX-300XDCS主控制卡的切换模式可分为（）

A.失电强制切换

B.失电强制切换，干扰随机切换和故障自动切换

C.失电强制切换和干扰随机切换

D.干扰随机切换和故障自动切换

A super drug that could remove Alzheimer’s (老年痴呆症)，heart disease and diabetes (糖尿病) and help people live to 100 is being developed by scientists. Their research is based on the identification of three genes that help prolong lives and prevent diseases which occur in old age. Medically controlling the proteins made by the “ longevity genes” will allow millions to live longer, predicts Dr Nir Barzilai.

Those whose DNA strongly features the three genes are 80 percent less likely to develop Alzheimer’s. The genes also fight against the deadly impact of smoking, poor diet, obesity and lack of exercise.

Already, several laboratories are working on a pill to imitate the benefits of the genes and Dr Barzilai thinks it could be tested within three years. The pill could remove some diseases that damage old age. “ The advantage of finding a gene that involves longevity is that we can develop a drug that will imitate exactly what this gene is doing,” he said.

Of the three longevity genes, two genes increase the production of so-called good cholesterol(胆固醇), which reduces the risk of heart disease. The third prevents diabetes. They were discovered by Dr Barzilai’s team while studying the DNA of 500 Ashkenazi Jews with an average age of 100. The chances of living that long are one in 10,000 but the group, which shared relatively few common ancestors, was 20 times more likely to hit the entury. Dr Barzilai said: “ 30 percent of them were obese or overweight and 30 percent smoked two acks of cigarettes a day for more than 40 years, however they can live to 100.”

But Andrew Ketteringham of the Alzheimer’s Society said: “Alzheimer’s disease, a most common disease, is likely to be caused by a combination of genetic disosition(遗传倾向), lifestyles and life events. Many genes are probably involved.

小题1:Some people are able to live to 100 years because of ______.

A．a magical medicine

B．three special genes

C．good living habits

D．longevity proteins小题2:Why does the discovery of the longevity genes mean a lot?

A．Because it can bring great benefits to scientific labs.

B．Because it can help people change their unhealthy genes

C．Because it helps produce a drug that can make people live longer.

D．Because it will help scientists build up a new branch of biology.小题3: From Paragraph 4 we can infer that ________.

A．longevity genes can create good cholesterol.

B．the volunteers share some common ancestors

C．bad habits are likely to have no effect on the volunteers

D．longevity genes protect the volunteers against bad habits小题4:What is Andrew Ketteringham’s attitude toward the study?

A．Positive

B．Negative

C．Critical

D．Cautious

遗传性痉挛性截瘫主要影响脊髓的哪个部位（）

A.皮质脊髓束

B.前庭脊髓束

C.脊髓后索

D.脊髓小脑束

E.以上均不正确

技师甲说：大多数变速器电磁阀安装在离合器壳外；技师乙说：大多数变速器电磁阀在拆卸时应作为一个总成拆卸。谁正确？（）

A、甲正确；

B、乙正确；

C、两人均正确；

D、两人均不正确。

钻头使用过程中，刃磨得到的顶角小于原始顶角时，主切削刃呈（）

A.直线

B.内凹曲线

C.外凸曲线

D.无规则变化曲线