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Is there intelligent lifeelsewhere in the Milky Way? The odds seem to favor apositive response．but scientists likenumbers and proofs．For tllat reason，radio astronomer Frank Drake created a formula that has becomefundamental for many Linein the field of SETI-the search for extraterrestrialintelligence．(5)The l961 Drake equation begins withN=the number of in tell igentcivilizations．defined asthose with whom we might communicate．It finds N bymultiplying the rate of star formation in our galaxy，whichDrake calculated as 10 per year。by the fraction ofstars with planets，about one．half．That in turn is multiplied by the number of planets per star thatmight be capable of sustaining(10)life，which Drakefigured as tw0，and by the fraction of those planetsthat will develop life．which he considered to be 100%．Finally, that is multiplied by the percentage of those life-bearingplanets that might develop intelligent life，thepercentage of that life that might be able to communicate．and the length of time during which such life might sendcommunications into space．Drake’s figures，(15) being 50 years old，have since been superseded by more accurate predictions．  
Which of these premises did Drake NOT includein his calculations?

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D．
Drake incorporated “the percentage of that life that might be able to communicate”(choice A)，“the length of time during which such life might send communications into space”(choice B)，“the number of planets per star that might be capable of sustaining life”(choice C)，and “the fraction of stars with planets”(choice E)．He did not include the satellites surrounding planets(choice D)，as that would presumably have no effect on intelligent life on planets．

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