Sentence 1: I had to take a math exam today. 
 Sentence 3: Just before the exam started, I realized I had not brought my pencil 
 Sentence 4:  I frantically asked everyone around me for a pencil 
 Sentence 5:  Fortunately, a friend lent me his pencil 
 Option 1: Since I had been studying for a week, I felt nothing could go wrong. 
 Option 2: I forgot about it until today and had not studied at all.