<p>That there A(exist) an infinite number of worlds B(outside) our solar system C(were) first hypothesized D(by the) sixteenth-century philosopher Giordano Bruno.</p>
<p>The answer is C. I understand that C should be "was", but why isn't A "exists" instead of "exist" because "number" is singular?!</p>
<p>Is infinite number of worlds singular or plural?</p>
<p>Rephrasing the sentence: Infinite number of worlds exists outside our world. So I believe that “exist” refers to the singular noun “number”. Am I right?</p>
<p>Is number singular or plural? There is a subtle distinction between “the number” by itself as “The number of cats is 12” where it’s singular, and in the phrase “a number of” as “a number of frogs are in the pond” where it is plural.</p>
<p>The phrase “an infinite number of words” is the second use, and in this case “number” is plural and hence “exists” rather than “exist”.</p>
<p>How could “number” be plural? Sorry, I haven’t understood this question yet. Would you please elaborate more?</p>
<p>Would you say “there is an abundance of cars” or " there are an abundance of cars". These sentences are quite the same as the original one. Am I right?</p>
<p>Do a search (using google or your favorite browser) for “phrase a number of”. You should find some clarifying articles on the difference between this use and the (more) common (and different) use with the definite noun “the number”.</p>
<p>This topic is a fine nuance in English and (in my opinion) not worth a great deal of attention in study for the SAT. I don’t ever expect that you’ll be tested on this usage.</p>
<p>Your example (with abundance) is not really the same as the original one with number. The rule I referenced is specific to “number”. abundance is singular.</p>
<p>Afaloo, the sentence, “There are an infinite number of galaxies,” is acceptable.</p>
<p>A similar sentence is, “There are a lot of cars on the freeway.”</p>
<p>The phrase “an infinite number of” is acting as an adjective, so the subject of the sentence is “galaxies.” Although it could be singular, it is not necessary to correct it since it is already grammatically correct.</p>
<p>I got it. Thank you so much!</p>