Animals were able to move and intermix with 26.
答案：(B) one another
one another 是相互代名詞，意思是「彼此」，本身就是完整的受詞，指所有動物之間互相往來混居；another 後面須接單數名詞或指「再一個」，other 是形容詞須接名詞，the other 指兩者中的另一個，三者都不合。
答對率僅 14%。
another、other、the other、one another 四個字長得像，你背下來的大概是「another＋單數名詞、other＋複數名詞、the other＝兩者中的另一個」這組規則，卻很少把 one another 當成一個「獨立的代名詞」記住——它的意思是「彼此、互相」，本身就是完整的受詞，後面不必再接名詞。
劍橋《English Grammar Today》把 each other 與 one another 並列為相互代名詞（reciprocal pronouns），用於主詞的成員彼此對對方做某件事。本句主詞 Animals 是複數，intermix（混居、往來）本身就是相互性的動作，需要的正是相互代名詞。中文的「互相」在英文裡不是副詞，而是要用代名詞放在受詞位置，這一點與中文語感差很多，是本題真正的難處。
another＝再一個、另一個，後面接單數名詞或單獨當代名詞（another cup／I want another）；other＝形容詞，後面一定要接名詞（other people）；the other＝兩者之中的另一個（one hand… the other hand）；one another／each other＝彼此、互相。本篇講的是整片超大陸上的眾多動物往來混居，不是兩隻動物互看。
interact／communicate／compete with one another（互相交流／溝通／競爭）、help each other（互相幫助）、one after another（一個接一個）、each other's + 名詞（彼此的…）。
Up to about 250 million years ago the world had just one huge super-continent called Pangaea. Animals were able to move and intermix with 26. About 200 million years ago this super-continent broke up into two continents: Laurasia and Gondwana. About 60 million years ago Gondwana broke up into 27 later became South America, Africa, Antarctica, India and Australia.
Since then Australia 28 from the rest of the world by vast oceans. The animals there no longer had 29 with animals from other parts of the world. They evolved separately. As a result, about 95 of Australia's mammals and 94 of its frogs are found 30 else in the world. Australia has lots of very unusual animals.