The extrem conditions of the weather in the icy land make 1.one imperative that emperor penquins join~.
The number of penguins assembed 2. is sometimes enormous, up to ten thousand~. ~which is very 3.densely packed penguins.However, emporer etiquette requires that no penguin 4.seek to advance himself~.It is all very democatic, for in fact 5.what looks like an immobile mass is really a very slowly revolving spiral~.문장을 조금씩 생략했습니다. 제 생각엔 1번이 it 이어야 할 것 같은데요. 가목적어로 that 이하가 진목적어구요...부탁드려요