Originally, there must have been just one type of ______________ on the Galapagos islands, but over time it diversified into man
y kinds, with different beak shapes. The same for tortoises. One type of ______________ must have turned into many kinds, with different shells depending on which island they lived on.
<em>"different </em><em>beak</em><em> shapes". </em>Beaks are often associated with birds.
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<em>"with different </em><em>shells</em><em>". </em>From the phrase and the one before <em>(The same for tortoises.)</em>, it is clear tortoises are the main topic.
