<p>Hey guys this question is really stumping me: </p>
<p>(Quick to)A (take advantage)B of Melanie Johnson's (preoccupation in)C the history of the Johnson family, the genealogist proposed investigating (that)D history for a price. </p>
<p>The answer is C </p>
<p>Why? It sounds right to me. What's the grammar rule?</p>