tube that protects it from the environment.

¡¡¡¡To make the caterpillar move forwards, Saga moves a magnetic field backwards along the caterpillar. Inside the caterpillar¬ðs ¡°head¡± capsule, magnetic fluid surges towards the attractive magnetic field, causing the capsule to bulge out to the sides and draw its front and rear portions up. As the magnetic field passes to the next capsule, the first breaks free and springs forward and the next capsule bunches up. In this way, the caterpillar can reach speeds of 4 centimeters per second as it crawls along.

¡¡¡¡Moving the magnetic field faster can make it traverse the caterpillar before all the capsules have sprung back to their original shapes. The segments then all spring back, almost but not quite simultaneously.

¡¡¡¡Saga plans to automate the movement of the caterpillar by placing electromagnets at regular intervals along the inside of its polymer tube. By phasing the current flow to the electromagnets, he¬ðll be able to control it wirelessly via remote control. He also needs to find a new type of rubber for the magnetic capsules, because the one he¬ðs using at the minute eventually begins to leak.

¡¡¡¡But crawling is not the most efficient form of locomotion for robots, says Robert Full of the University of California at Berkeley, an expert in animal motion who occasionally advises robotics designers. ¡°If you look at the energetic cost of crawling, compared to walking, swimming or flying, crawling is very expensive,¡± he says. Walking, on the other every step, energy is conserved in the foot and then released to help the foot spring up.

¡¡¡¡Saga acknowledges this inefficiency but says his caterpillar is far more stable than one that walks, rolls on wheels or flies. It has no moving parts save for a few fluidª²filled rubber capsules. Biped robots and wheeled robots require a smooth surface and are difficult to miniaturize, and flying robots have too many moving parts. ¡°My peristaltic crawling robot is simple ¡ª and it works,¡± he says.

¡¡¡¡1. From this passage, we can learn that .

¡¡¡¡A. A robotic caterpillar can crawl by a pair of rubber rods.

¡¡¡¡B. When a caterpillar moves, the magnetic field moves backwards along it.

¡¡¡¡C. The environment couldn¬ðt influence a robotic caterpillar¬ðs guts, which are wrapped in a capsule.

¡¡¡¡D. Crawling is very stable and efficient, and when it moves, only a few elements are needed.

¡¡¡¡2. According to this passage, which is not TRUE about the construction of the robotic caterpillar?

¡¡¡¡A. A robotic caterpillar is made from a series of rubber capsules filled with a magnetic fluid.

¡¡¡¡B. Iron particles, water, and a detergentª²like surfactant form a magnetic fluid.

¡¡¡¡C. Each capsule filled with a magnetic fluid is linked to a pair of rubber rods.

¡¡¡¡D. In order to keep stable condition, the caterpillar¬ðs guts are wrapped in a clear, flexible polymer tube.

¡¡¡¡3. The meaning of the word ¡°peristalsis¡± in p

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