<p>Why D and not B? I think the 'if' in option B is a bit weird.</p>
<p>Two problems with B.</p>
<p>First, "their" is unclear. Who is they? The candidates or their opponents? (That's why all the other options specify the subject, rather than use a pronoun.)</p>
<p>Second, the grammar pattern of "Their goal...would be if" is not correct.</p>
<p>Should be something like "Their goal...is to XXX."</p>
<p>This correct grammar pattern occurs in D: "The goal...is to win elections."</p>