<p>Sorry about the misleading title. Yes, this is must read because I said so.</p>
<p>By using electromagnetic sensors to record the frequency of lightning strikes throughout the United States, meteorologists have determined that it occurs at the rate of 2,000 per hour.</p>
<p>Does someone want to explain why D is wrong? I feel as though the question is vague as I feel that it should refer to frequency, but apparently it doesn’t.</p>
<p>Anyways, expound por favor.</p>
<p>refers to “frequency OF lightning strikeS”</p>
<p>“D” refers to “Lightning strikes”, which is plural. It occurs—>They occur</p>
<p>13dwang is correct. When tackling questions like these, always make sure that the verb in the sentence agrees with its subject.</p>
<p>To answer the concern with the ambiguity of it, it cannot refer to the frequency because “frequency occurs at the rate of 2000 per hour” would not be logical. It would be redundant to say that since frequency is the occurrence. Therefore, you must conclude that the pronoun refers to the lightning and should be “they occur”.</p>