<li><p>Although the directions that they sent out with the invitations show an easy way to get to their house, there is actually several different ways to get there faster by taking the back roads.</p></li>
<li><p>A high concentration of radioactive chemicals and other contaminants have been found in the drinking water at ETS headquarters, which may have caused brain damage in some of its test writers.</p></li>
<li><p>An understanding of irony and sarcasm are usually the last steps in learning a language.</p></li>
<li><p>Sensationalism in television shows masquerading as “news” programs are making it difficult for serious journalism to compete for ratings.</p></li>
</ol>
<p>Although the directions that they sent out with the invitations show an easy way to get to their house, there **is* actually several different ways to get there faster by taking the back roads.*</p>
<p>Ways is plural. It should be "are."</p>
<p>A high **concentration* of radioactive chemicals and other contaminants have been found in the drinking water at ETS headquarters, which may have caused brain damage in some of its test writers.*</p>
<p>Concentration is singular. It should be "has."</p>
<p>An **understanding* of irony and sarcasm are usually the last steps in learning a language.*</p>
<p>Understanding is singular. It should be "is."</p>
<p>**Sensationalism* in television shows masquerading as "news" programs are making it difficult for serious journalism to compete for ratings.*</p>
<p>Sensationalism is singular. It should be "is."</p>
<p>Thanks so much. I get confused when the noun and verb are so far apart and I can't seem to distinguish which verb is for which noun.</p>
<p>ignore prepositional phrases</p>
<p>Yup, read the sentence without the prepositional phrases and it should be much easier.</p>
<p>What do you mean by "prepositional phrases"? What are they? Do they just describe the noun in-depth or something?</p>
<p>"A high concentration of radioactive chemicals and other contaminants have been found in the drinking water at ETS headquarters, which may have caused brain damage in some of its test writers."</p>
<p>This is the above sentence without prepositional phrases:</p>
<p>"A high concentration have been found, which may have caused brain damage."</p>
<p>Now, is the error more obvious?</p>