<p>For #25, P.783, Blue Book:</p>
<p>(a) For the past hundred years or more, Yellowstone National Park (b) was a kind of sociological laboratory (c) in which North Americans have been exploring the (d) the meaning of the national-park concept. (e) No error</p>
<p>The answer is B, but I'm not really sure why. Any help would be appreciated!</p>
<p>should be "has been" since it still is a socialogical laboratory.</p>
<p>Think of a simple situation:</p>
<p>Incorrect: For the last six years, George Bush was President of the U.S.</p>
<p>Correct: For the last six years, George Bush has been President of the U.S.</p>
<p>"Was" generally means whatever it is you are talking about is no more. "Has been" is used when the situation is continuing.</p>