<p>(The eerie songs of humpback whales, often lower in pitch and longer than birds,) are intriguing to scientists partly because whales have no functional vocal cords.</p>
<p>I put (c) Humpback whales' eerie songs, often pitched lower and longer than that of birds,</p>
<p>however, the answer is (d) The eerie songs of humpback whales, often lower in pitch and lasting longer than those of birds,</p>
<p>For choice (c), ‘that’ can not modify the ‘eerie songs.’ For example you wouldn’t say “that eerie songs,” you would say “those eerie songs.” That is why D is correct</p>
<p>Does it matter which way the beginning of the sentence is? Is there any difference between: The eerie songs of “humpback whales” and “Humpback whales’ eerie songs”</p>