Sentence 1: I had always wanted a dog, but was waiting until I had a teaching job. 
 Sentence 3: She had a litter of puppies she was giving away 
 Sentence 4:  I decided to take the little male puppy, who couldn't find a home 
 Sentence 5:  He happily came to live with me that day 
 Option 1: On the day I officially became a teacher, I met a student. 
 Option 2: On the day I became a teacher, I bought a dog.