<ol>
<li>Researchers have found that large fish [are most likely to contain high levels of mercury than small fish].</li>
</ol>
<p>(C) are more likely than small fish to contain high levels of mercury
(E) more likely contain higher levels of mercury than in small fish</p>
<p>C because it correctly uses “more” to compare two things. The original uses “most”, which is only used for 3+ things. E is wrong because there is no verb.</p>
<p>C. Though people often would move the phrase “than small fish” to the end in conversation, it’s grammatically correct either way.</p>
<p>E has a few problems. First of all, “more likely contain higher levels” is a bit off. If you replace the words with parallels and say “US gymnasts more likely win than Chinese gymnasts,” the problem becomes much more apparent. You would say “are more likely to”.
Also, the sentence shouldn’t have “more likely” and “higher”, just one or the other. When you add the second comparison, the sentence loses its meaning.
Last, the “in” doesn’t belong. When you use the “than” comparison, what you’re really saying is “large fish are more likely to contain high levels of mercury than small fish are likely to contain high levels of mercury.” Though that obviously doesn’t sound right because the point of “than” is that you get rid of the last part, adding the word “in” makes it much worse.</p>
<p>…spellweaver’s explanation is a heck of a lot simpler than mine. Oh well!</p>
<p>Thank you both :)</p>
<p>And amelia, you cleared up some questions I still had, so thank you for your long response!</p>