In the Cascade mountains of California, north f Lassen Peak, astronomers are looking for aliens. The Allen Telescope Array ___1_ of 42 dish antennas, each six meters across,scattered across the countryside. When the array is complete, it will have 350 dishes that, by acting in __2__ , will have the power of a single instrument 700 meters across. The Allen telescope is looking for aliens the __3___ way: by searching for radio signals that have either been sent out ____4__, or leaked into space accidentally, as human radio signals are. The search for extraterrestrial intellegence, or SETI, is a 50-year-old idea. Much progress has been made in ___5____Earthlike planets but about 1000 star systems have also been subject to serious radio scrutiny. The Allen array will increase the number to 1m within a decade. That is an ___6___ number but some think this is the wrong approach. Paul Davies, a physicist at Arizona State University, points out that wide-spread radio communications may prove a short-lived historical __7____ on Earth. Humans are, after all, increasingly using fibre optics to talk to each other.____8___ , many modern radio devices rely on a technique called "spread spectrum" encoding. It uses signals that look like background noise, except to a receiver equipped with the right unscrambling code. Humans figured this out within a century of __9___ radion technology, so aliens might have done the same. Radio signals that are clearly artificial in origin may, then, be only a transient sign of civilizaion. So it might make ___10___ to widen the search by looking for other telltales. A. comprises B. deleberately C. impressive D. concert E. Moreover F. inventing G. together H. occassionally I. locating J. phenomenon K. traditional L. sense M. trival N. But O. consists