A. Push the move B. Keep the level

　　C. Control the rise D. Break the balance

5. The government's new measures will greatly benefit _____.

A. pharmacy owners B. local merchants C. new parents D. adult users

C.

　　Listen carefully to the footsteps in the family home, especially if it has wooden floors, and you can probably work out who it is that is walking about. The features most commonly used to identify people are faces, voices, finger prints and retinal scans. But their "behavioural biometrics", such as the way they walk, are also giveaways.

　　Researchers have, for several years, used video cameras and computers to analyse people's gaits, and are now quite good at it. But translating such knowledge into a practical identification system can be tricky----especially if that system is supposed to be hidden. Cameras are often visible, are hard to set up, requi5re good lighting and may have their view blocked by other people. So a team led by Krikor Ozanyan of the University of Manchester, in England and Patricia Scully of the National University of Ireland, in Galway have been looking for a better way to recognize gait. Their answer: pressure-sensitive mats.

　　In themselves, such mats are nothing new. They have been part of security systems for donkeys' years. But Dr. Ozanyan And Dr. Scully use a complex version that can record the amount of pressure applied in different places as someone walks across it. These measurements form a pattern unique to the walker. Dr. Ozanyan and Dr. Scully therefore turned, as is now common for anything to do with pattern recognition, to an Artificial Intelligence system that uses machine learning to recognize such patterns.

　　It seems to work. In a study published earlier this year the two researchers tested their system on a database of footsteps trodden by 127 different people. They found that its error rate in identifying who was who was a mere 0.7%. And Dr. Scully says that even without a database of footsteps to work with the system can determine someone's sex---women and men, with wide and narrow pelvises(骨盆) respectively, walk in different ways,---- and guess, with reasonable accuracy, a subject's age.

　　A mat-based gait-recognition system has the advantage that it would work in any lighting conditions----even pitch-darkness. And though it might fail to identify someone if, say, she was wearing stilettos and had been entered into the database while wearing trainers, it would be very hard to fool it by imitating the gait of an individual who was allowed admission to a particular place.

　　The latest phase of Dr. Ozanyan's and Dr. Scully's project is a redesign of the mat. The old mats contained individual pressure sensors. The new ones contain optical fibres(光纤). Light-emitting diodes(二极管) distributed along two neighbouring edges of a mat transmit light into the fibres. Sensors on the opposite edges( and thus the opposite ends of the optical fibres) measure how much of that light is received. Any pressure applied to part of the mat causes a distortion(变形) in the fibres and a consequent change in the amount of light transmitted. Both the location and amount of change can be plotted and analyzed by the machine-learning system.

Dr. Ozanyan says that the team have built a demonstration fibre-optic mat, two meters long and a metre wide, using materials that cost ￡100($130). They are now talking to companies about commercializing it. One application might be in health care, particularly for the elderly. A fibre-optic mat installed in a nursing home or an old person's own residence could monitor