Sentence 1: Mack was leaving for college. 
 Sentence 3: All Mack's friends had received new cars, but Mack expected nothing 
 Sentence 4:  Then, as he was packing, his dad handed him a key 
 Sentence 5:  Mack looked outside and saw his gift - his own new (used) car! 
 Given Sentence 2: But his parents were poor, so he didn't expect an extravagant gift.