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更多“Drilling holes in some large and heavy workpieces on the radial drilling machine, the workpiece is f…”相关的问题
A、Larva migration in human body
B、Adults have the habit of drilling holes
C、Adult predatory nutrition
D、Adults secrete toxins
According to the passage, the new drill
A．can't drill holes in different cross-sections.
B．needs significant weight on the bit when drilling the hardest rocks.
C．needs more watts of power though it is cheaper than rotary drill.
D．can work well in a range of temperatures from extremely cold to very hot.
A．The microorganisms brought up were of a species that is related to those previously known to science.
B．No holes have been drilled into the Earth" s surface to a distance deeper than 1. 74 miles.
C．The microorganisms did not come from surface soil that came into contact with the drilling equipment.
D．The stratum from which the samples came has been below the surface of the Earth ever since the Earth came into existence.
E．The temperature at the bottom of the holes drilled was not significantly hotter than that of the hottest spots on the Earth"s surface.
Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. (40 points)
A tiny but powerful new lightweight drill has been developed by space scientists and engineers. It expands the fields in which drilling has been difficult in the past. The new drill could be used in the drilling required during surgical or diagnostic procedures involving bones, or when extracting heart pacemaker leads. Future space missions could include drilling for rock and soil samples, using only lightweight landing vehicles with robotic arms.
The color photo shows the new driller penetrating a sandstone while the drill is held only from its power cord. Relatively small vertical force is used in this application—a factor that will be useful when the drill is used in future space missions and weight needs to be kept to a minimum. The drill is driven by piezoelectric devices, which have only two moving parts but no gears or motors. Piezoelectrics are materials that change their shape under the application of an electrical field. The drill can be adapted easily to operations in a range of temperatures from extremely cold to very hot. Unlike conventional rotary drills, the drill can drill even the hardest rocks without significant weight on the drilling bit.
"The drill is a device that offers exciting new capabilities for space exploration in future NASA missions," said Dr. Yoseph Bar-Cohen, who leads NASA's Jet Propulsion laboratory's Nondestructive Evaluation and Advanced Actuator Technologies unit. "Besides the immediate benefits of the technology to NASA, it is paving the way for other unique mechanisms that are being developed in our laboratory and elsewhere," he said.
The demonstration unit pictured in the color photograph weighs about 0.7 kilograms, which is sufficient to drill 12 millimeter diameter holes in rocks using less than 10 watts of power. Comparable rotary drills usually require the application of 20 to 30 times greater pushing force and more than three times the power.
Other advantages to the drill are no drill noise and no drill movement across the surface on start-up. The drill body will not rotate, the speed does not decrease with time and the bit does not require sharpening. The bit can be guided by hand safely during operation. The drill can drill holes in different cross-sections, such as square and round.
Said Dr. Yoseph Bar-Cohen, "Thanks to the development of technology associated with this drill, new devices can be made to be small and lightweight, to consume little power and to exhibit a high standard of reliability."
At first, the new lightweight drill has been invented to
A．be used in space missions.
B．pull out the heart pacemaker leads.
C．replace the conventional rotary drill.
D．drill the bones during procedures of medical treatment.
Why can't you see light when you look at a black hole？
A．Because most black holes are so far away.
B．Because the gravity of a black hole is so strong that it sucks the light inward.
C．Because as the star's gases burn, it stops giving off heat and light.
D．Because as a star cools, its outer layers pull in toward its center.
According to this passage, holes were made in train tickets so as to______.
A．show that the tickets were correct
B．give a picture of the person who owned the ticket
C．show how much the tickets cost
D．record the details of a train robbery
根据下面材料，回答题。
Black Holes
Most scientists agree that black holes exist but are nearly impossible to locate. A black hole in the universe is not a solid object, like a planet, but it is shaped like a sphere (球体). Astronomers(天文学家) think that at the center of a black hole there is a single point in space with infinite (无限的) density (稠密). This single point is called a singularity (奇点). If the singularity theory is correct, it means that when a massive star collapses, all the material in it disappears into the singularity. The center of a black hole would not really be a hole at all, but an infinitely dense point.
Anything that crosses the black hole is pulled in by its great gravity.
Although black holes do exist, they are difficult to observe. These are the reasons.
？ No light or anything else comes out of black holes. As a result, they are invisible to a telescope.
？ In astronomical terms, black holes are truly. For example, a black hole formed by the collapse of a giant star would have an event horizon (视界) only 18 miles across.
？ The nearest black holes would be dozens of light years away from Earth. One light year is about 6 trillion (万亿) miles. Even the most powerful telescopes could not pick out an object so small at such a great distance.
In 1994 the Hubble Space Telescope provided evidence that black holes exist. There are still answers to be found, however, so black holes remain one of the mysteries of the universe.
Black holes are part of space. 查看材料
A.Right
B.Wrong
C.Not mentioned
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