<p>I don't have an answer key so please give me the right answer and an explanation :) </p>
<ol>
<li><p>A wingspan (of) eight feet (makes) the trumpeter swan , which (once) ranged the entire North America continent, the world's (largest) species of waterfowl. </p></li>
<li><p>Traces of bronze on metalworking waste products (unearthed by) archaeologists (indicate) that ancient Britons (melt down) Roman coins and refashioned them into trinkets (to sell) back to the Romans. </p></li>
<li><p>(Contrary to) a common perception, science fiction has always been (preoccupied with) the present day (using) futuristic plots merely as a (means of exploring) contemporary issues. </p></li>
<li><p>The "USDA" sticker (found on) some vegetables (serves) to (insure) shoppers that those vegetables were (grown) without the use of synthetic pesticides.</p></li>
</ol>