题目内容
（请给出正确答案）
提问人：网友wu10wu10
发布时间：2022-01-07
[主观题]
Lightweight gears would make the process from ascending to descending more comfortable and convenient.
简答题官方参考答案
（由简答题聘请的专业题库老师提供的解答）
查看官方参考答案
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.
