Sentence 1: Sam was doing his physic homework. 
 Sentence 3: Apparently the page had been torn out 
 Sentence 4:  Sam was able to find a copy of the page he needed online 
 Sentence 5:  Sam completed his homework and got an outstanding grade 
 Option 1: He noticed that his textbook was missing. 
 Option 2: He noticed that the assignment in his textbook was missing.