题目

 阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。  The Search for Extraterrestrial Intelligence (SETI) Institute is America's only (science) organization that investigates life on other planets. Project Phoenix, is SETI's main research project, uses the world's most advanced equipment to look at outer space. They look especially for signals on the microwave band from 1,000 MHz to 3,000 MHz, the band that researchers believe life on other plants could use to get touch with us. Project Phoenix has not detected any extraterrestrial (外星的) signals yet. If an unusual signal is discovered, the scientists must be able (keep) track of it. In 1977, an unusual signal was heard at the Ohio State Radio Observatory. (unfortunate), the signal was irrelevant to life. The signal was never heard again. Nothing like this (happen) at SETI since then. In the (absent) of such signals, no one could tell whether there is any other life form out there in space. But what if SETI discovered a signal? Would they reply to the signal? Right now, SETI does not plan to reply to any signals they might discover. If they heard a signal, the nations of the Earth would have to decide whether not to reply. This means senders of signal may never know the Earth received their signal. Also, it's never easy to send signals back. The receivers would be very far away, and it (take) many years for the signals to travel to them. 答案：【1】scientific【2】which【3】into/in【4】to keep【5】Unfortunately【6】has happened【7】absence【8】or【9】the【10】would take

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