问题 单项选择题

X线管阳极靶面所用的物质必须具有()。

A.低原子序数,高熔点

B.低原子序数,低熔点

C.高原子序数,高熔点

D.高原子序数,低熔点

E.低密度、高比重

答案

参考答案:C

解析:靶面材料应具备以下条件:原子序数高、X线发生效率高、熔点高、金属蒸发率低、导电率高以及热传导率高。

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     A few years ago, Paul Gerner began to gather a group of architects in Las Vegas to ask them what it

would take to design a public school that used 50 percent less energy, cost much less to build and obviously

improved student learning. "I think half of then fell off their chairs," Gerner says.

     Gerner manages school facilities (设施) for Clark county, Nevada, a district roughly the size of

Massachusetts. By 2018, 143, 000 additional students will enter the already crowded public-education system.

Gerner needs 73 new schools to house them. Four architecture teams have nearly finished designing primary

school prototypes (样品); They plan to construct their schools starting in 2009. The district will then assess

how well the schools perform, and three winners will copy those designs in 50 to 70 new buildings.

     Green schools are appearing all over, but in Clark County, which stands out for its vastness, such

aggressive targets are difficult because design requirements like more natural light for students go against the

realities of a desert climate. "One of the biggest challenges is getting the right site orientation (朝向)," Mark

McGinty, a director at SH Architecture, says. His firm recently completed a high school in Las Vegas. "You

have the same building, same set of windows, but if its orientation is incorrect and it faces the sun, it will be

really expensive to cool."

     Surprisingly, the man responsible for one of re most progressive green-design competitions has doubts

about ideas of eco-friendly buildings. "I don't believe in the new green religion," Gerner says. "Some of the

building technologies that you get are impractical. I'm interested in those that work." But he wouldn't mind

if some green features inspire students. He says he hopes to set up green energy systems that allow them to

learn about the process of harvesting wind and solar power." "You never know what's going to start the

interest of a child to study math and science," he says.

1. How did the architects react to Garner's design requirements?

A. They lost balance in excitement.

B. they showed strong disbelief.

C. they expressed little interest.

D. they burst into cheers.

2. Which order of steps is followed in carrying out the project?

A. Assessment-Prototype-Design-Construction.

B. Assessment-Design-Prototype-Construction.

C. Design-Assessment-Prototype-Construction.

D. Design-Prototype-Assessment-Construction.

3. What makes it difficult to build green schools in Clark County?

A. The large size.

B. Limited facilities.

C. The desert climate.

D. Poor natural resources.

4. What does Gerner think of the ideas of green schools?

A. They are questionable.

B. They are out of date.

C. They are advanced.

D. They are practical.

多项选择题