<p>I’m not really sure how I understood these two, but it was something along the lines of the following:</p>
<p>One, in the first example, was preceded by ‘the’ and it refers to Jason. Therefore, one defined something in particular which makes it the core of the sentence, and not “of the three people”. I think this is what an adjectival prep. phrase is?</p>
<p>In the second example, one, does not define anything or anyone in particular. It simply modifies the core of the sentence which is ‘of the five girls’, therefore ‘who’ actually refers to ‘of the five girls’, and not ‘one’. I think this is what an adjectival clause is?</p>
<p>I’m not sure of this, but that’s what I could infer.</p>