<Dl> <Dd> The factor depends on what generally is the cause of civilization extinction . If it is generally by temporary uninhabitability, for example a nuclear winter, then n may be relatively high . On the other hand, if it is generally by permanent uninhabitability, such as stellar evolution, then n may be almost zero . In the case of total life extinction, a similar factor may be applicable for f, that is, how many times life may appear on a planet where it has appeared once . </Dd> </Dl> <Dd> The factor depends on what generally is the cause of civilization extinction . If it is generally by temporary uninhabitability, for example a nuclear winter, then n may be relatively high . On the other hand, if it is generally by permanent uninhabitability, such as stellar evolution, then n may be almost zero . In the case of total life extinction, a similar factor may be applicable for f, that is, how many times life may appear on a planet where it has appeared once . </Dd> <Dl> <Dt> METI factor </Dt> <Dd> Alexander Zaitsev said that to be in a communicative phase and emit dedicated messages are not the same . For example, humans, although being in a communicative phase, are not a communicative civilization; we do not practise such activities as the purposeful and regular transmission of interstellar messages . For this reason, he suggested introducing the METI factor (messaging to extraterrestrial intelligence) to the classical Drake equation . He defined the factor as "the fraction of communicative civilizations with clear and non-paranoid planetary consciousness", or alternatively expressed, the fraction of communicative civilizations that actually engage in deliberate interstellar transmission . </Dd> </Dl> <Dd> Alexander Zaitsev said that to be in a communicative phase and emit dedicated messages are not the same . For example, humans, although being in a communicative phase, are not a communicative civilization; we do not practise such activities as the purposeful and regular transmission of interstellar messages . For this reason, he suggested introducing the METI factor (messaging to extraterrestrial intelligence) to the classical Drake equation . He defined the factor as "the fraction of communicative civilizations with clear and non-paranoid planetary consciousness", or alternatively expressed, the fraction of communicative civilizations that actually engage in deliberate interstellar transmission . </Dd>

Which of the following factors in the simplified drake equation is best known