<p>For the first one, “data” are plural. The singular is “datum.” So it’s “tell” not “tells.”</p>
<p>The second one, I believe, is an issue of tenses. The words “thought” and “was” are simple past, so the “ever had” part should be in the past perfect, i.e. “had ever had.” (Weird, I know.) Alternatively, it could be “I think your chocolate cake is the best I have ever had,” but you can’t get to that without changing 3 parts of the sentence.</p>
<p>the OP is correct about the first one… the error is a tense error, not a singular/plural agreement error. Data could be either singular OR plural, but because the sentence starts “to this day,” the present tense “tells” wouldn’t work.</p>
<ol>
<li><p>“tells” should be “has told”: To this day, Jane Goodall’s data on primate behavior has told us a lot about the similarities between monkeys and humans.</p></li>
<li><p>“thought” should be “think”: For what it’s worth, I think your chocolate cake was the best cake I ever had!</p></li>
</ol>
<p>I’m not certain what CB thinks of “data.” They do tend to be fairly conservative about language, however, and the more conservative usage would treat “data” exclusively as the plural. “Data” in the singular would be the Star Trek character. </p>
<p>On the other hand, the use of “data” as a singular collective noun, to refer to a mass of information, is accepted by several reasonably authoritative sources; but there are quite a few publishers who still won’t permit this use–to say nothing of the science profs for whom I used to write papers. Does anyone have an official CB source that shows how CB construes “data?”</p>
<p>“To this day” means it is still telling us. The past tense wouldn’t work.The decision is between tell - tells or no error. It depends on if data is/are plural or not according to CB.</p>
<ol>
<li>“Tells” should be “has told” (which is still present tense!) because of “To this day…”
I’d say it should be “tell” if it weren’t for that beginning phrase, but either way, B is the right answer.</li>
<li>“Ever had” should be “had ever had”; “thought” should NOT be changed to “think” because everything else is already in the past tense. Changing that would cause a conflict in verb tense.</li>
</ol>
<p>No, I think “thought” should be changed to “think”, because “for what it’s worth” equals “for what it is worth” which is present. So basically, if you substitute “thought” for “think,” the you are saying “for what it is worth, I think…[it] was the best…I ever had!”</p>
<p>First part is present, then you think back and say “it was the best thing I ever tasted.”</p>