真核生物中tRNA和5SrRNA的转录由下列哪种酶催化() A.RNA聚合酶Ⅰ B.

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问题:

真核生物中tRNA和5SrRNA的转录由下列哪种酶催化()

A.RNA聚合酶Ⅰ

B.反转录酶

C.RNA聚合酶Ⅱ

D.RNA聚合酶全酶

E.RNA聚合酶Ⅲ

考点:上海住院医师康复医学科上海住院医师康复医学科题库
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简述程控放大的工作过程。

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有A、B、C、D四种短周期元素,它们的原子序数由A到D依次增大,已知A和B原子有相同的电子层数,且A的L层电子数是K层电子数的两倍,C单质燃烧时呈现黄色火焰,C的单质在点燃时与足量的B单质充分反应,可以得到与D单质颜色相同的淡黄色固态化合物,试根据以上叙述回答:

(1)C离子结构示意图:______.

(2)AB2的结构式为______.

(3)C2D的电子式:______.

(4)写出由B、C、D三种元素组成的两种化合物的化学式______,______.

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斜井人车发生断绳时,跟车工应打停车点。

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固态金属的冷变形和热变形

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Raymond Arth knows he should feel better about the economy. His company hasn’t returned to its pre-recession revenues selling its wares to the makers of RVs and manufactured homes, but it is making a profit again. Like too many other small-business proprietors, Arth doesn’t fully trust this economic recovery. While he says he’s "guardedly optimistic" about it, his actions are all about the first half of that phrase,

In the Labor Department’s latest snapshot of the country’s job market, the private sector added 268,000 jobs in April, the largest gain in five years and the third consecutive month of solid job growth. Yet a more sobering account of where the economy might be headed—and arguably a more accurate barometer of the near-term future—is the monthly report published by the National Federation of Independent Business. After all, it’s small businesses, which have created two out of every three new jobs the economy has added since the early 1990s, that historically have led the country out of recessions. And it’s the owners of small businesses that the NFIB surveys each month for its Small Business Optimism Index.

On that front the news is anything but good. The index is down for the second straight month. Fewer small-business owners expect conditions to improve over the next half year a drop of 18 percentage points from January. The bulk of new hiring must be happening inside larger corporations, since their smaller counterparts on Main Street say they are generally reluctant to create new jobs. That aptly sums up the sentiments of Scott Lipps, the president of the Sleep Tite Mattress Factory. Before the downturn, Lipps says, his sales were about evenly split between his medical clients (hospitals and nursing homes) and consumers buying mattresses through a factory outlet. But sales to the general public plummeted starting in 2008.

"The families affected most by the economy have stopped buying," Lipps says. "And those who say ’We have to have a new mattress’ are downgrading to a medium-quality mattress. " Despite a 20 percent drop in sales, Lipps and his partner tried to forestall the inevitable by putting up $ 70,000 of their own money. But in 2010 they laid off three of their 18 full-time employees. "It should have happened in 2009, but we let our hearts run the company instead of our billfolds," Lipps says.

In Bartlesville, Mat Saddoris is feeling relatively more upbeat. Saddoris is the third-generation owner of United Linen, a restaurant-supply company that cut its workforce by more than 10 percent during the downturn’s darkest days. Revenues are back up to pre-2008 levels, and United Linen is back to its pre-recession staffing of 135 employees. But will he take the risk of growing the company "I talk to my customers and they’re optimistic—to a point," he says. "They’ve all come back from the pits, if you will, and things have been getting better in the past six or seven months. " But, he says, "I don’t think they’re ready to announce that things have turned around. \

What Scott Lipps says explains()

A. why small businesses are cautious in hiring people

B. why small businesses have not generated a profit

C. how the federal economic policies affect small businesses

D. how customers have changed their buying habits

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