Sentence 1: Rachael and Kristy were best friends. 
 Sentence 3: Mark broke up with Rachel for no reason 
 Sentence 4:  The next week Mark and Kristy started dating 
 Sentence 5:  Rachael and Kristy are no longer best friends 
 Option 1: Rachael was dating a boy named Mark. 
 Option 2: Kristy was dating a boy named Mark.