某大型项目进行到两年时，使用挣值法所需的三个中间变量的数值分别是：计划值PV为400万元，实际成本AC为200万元，挣值EV为100万元。基于该项目的成本偏差，下列描述中正确的是 38 ；...变更管理首要完成的任务是______。
A.分析变更的必要性和合理性，确定是否实施变更
B.记录变更信息，填写变更控制单
C.做出更改，并交上级审批
D.修改相应的软件配置项(基线)，确立新的版本
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Thigh, robot People who have suffered debilitating strokes often have to cope with impaired muscles that do not work properly. Even a simple act such as standing up from a chair and walking a few steps can become extremely difficult. Stroke victims often have to rely on wheelchairs, sticks, walking frames and other "orthotic" devices to move about. But a new generation of active orthotic devices, capable of augmenting or replacing lost muscle function, is in the works. These devices use an assortment of complex computer and mechanical technology, borrowed from the field of robotics, to help patients get around. They are being made possible by the falling prices and improving performance of sensors, computer control systems and battery technology. As well as benefiting elderly patients with permanent paralysis or muscle dysfunction, such devices could also help people in recovering from "arthroscopic" (literally, "looking within the joint") operations. Around 850,000 arthroscopic and knee replacement operations are carried out each year in America alone, and patients require an average of six weeks of rehabilitation before they are fully mobile again. Active orthotic devices could get them back on their feet sooner. Designing such devices presents a number of challenges. The biggest problem is providing enough power to assist the wearer, without making the device too bulky and heavy. Another challenge is devising a responsive and unobtrusive control system that can take readings from several sensors and automatically respond to the wearer’’s motion by making appropriate movements. Several start-ups are, however, rising to the challenge and readying products for market. Among the firms developing active orthotic devices is Tibion, based in Moffett Field, California. It has developed the PowerKnee, a medical device that augments muscle strength in the quadriceps to help the wearer stand, walk and climb stairs. The device is based on recent advances in portable computing, embedded systems, prosthetics and materials, and Tibion expects it to be submitted for regulatory approval next year. America’’s space agency, NASA, has expressed interest in it, since muscle—augmentation systems might enable astronauts to work in space for longer without getting tired. Another company working in this area is Yobotics, based in Boston, Massachusetts, which has developed a powered device called the RoboKnee. It allows a healthy wearer to perform deep knee — bends indefinitely — or, at least, until the batteries run out. This is intended to be a first step towards the development of a far more elaborate exoskeleton device, the RoboWalker, which will augment or replace the muscular functions of the lower body. Also working on active orthotic devices is Hugh Herr of the Massachusetts Institute of Technology (MIT). His team has designed an ankle brace to assist people with "drop foot", who are unable to lift their feet normally when walking, because of weakened or damaged muscles around the ankle. The battery-powered device, which uses a motor to help raise and lower the front of the foot as the heel strikes the ground and lifts again, is about to begin testing on patients. Also at MIT, Woodie Flowers, a mechanical engineer, is developing an active joint brace that is designed to function like an active exoskeleton. Perhaps the best-known example of such a device is the exoskeleton seen in the film "Aliens", which allows the wearer to move heavy objects around, rather like a fork-lift truck. This kind of technology may not, it seems, remain in the realm of science fiction for much longer.
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