第二空要填 extinction
前面说significant fluctuations in climate and physical conditions (气候和环境的重大变动),后面说without which (没有变动),the ____ of species should be rare (物种的___应该很少见)
transmission (传送;播送)
extinction (灭绝)
advancement (进步;提升)
从这三个词的意思来看,最合适的就是extinction,因为重大气候变化能引起动物灭绝(如恐龙).