I am a senior in high school. For four years I have been a member of the marching band at my school---four years of commitment to an organization of 150 kids, four teachers and 100 parents working from August to June of every school year. For four years, my mom has been there for me---never complaining and never receiving a "Thanks, mom." My mom is pretty much a supermom and, unfortunately, it took me some seventeen years to realize it. "Driver" is probably a more appropriate name for her. Every concert, every competition, every football game, my mom was there with a smile, and always stayed to watch. When she couldn't be there, she would be waiting for me when the bus pulled in to the school's parking lot. She actually enjoyed arriving at the school at 10:30 at night just for me to tell her that I was going out with my friends and that I needed twenty dollars instead of a ride home. Now that I'm a senior, I have my own car and drive myself to my football games and concerts. My mother still comes to watch me.  Recently, my band was invited to play for a celebration. When the bus pulled up to the flagpole in front of my high school, I had the strangest feeling. Something was missing. I found myself nervously searching for my mom in the parking lot. I needed to tell her I didn't need a ride home; I was going out. I then realized my mother was at home and probably in bed. I never realized how much I took her for granted until she wasn't there. When I got home that night, I woke her up and told her I loved her and I missed her. I told my mom that I really appreciated all the times she had driven me back and forth. I told her I was glad she embarrassed me all those times, because I knew that it just meant she loved me, too. My mom looked back at me with tears and a big smile. The author realized his mother's love when   _  .
he was a child he graduated from senior high school he couldn't find her one day his mother was sleeping
Question: I am a senior in high school. For four years I have been a member of the marching band at my school---four years of commitment to an organization of 150 kids, four teachers and 100 parents working from August to June of every school year. For four years, my mom has been there for me---never complaining and never receiving a "Thanks, mom." My mom is pretty much a supermom and, unfortunately, it took me some seventeen years to realize it. "Driver" is probably a more appropriate name for her. Every concert, every competition, every football game, my mom was there with a smile, and always stayed to watch. When she couldn't be there, she would be waiting for me when the bus pulled in to the school's parking lot. She actually enjoyed arriving at the school at 10:30 at night just for me to tell her that I was going out with my friends and that I needed twenty dollars instead of a ride home. Now that I'm a senior, I have my own car and drive myself to my football games and concerts. My mother still comes to watch me.  Recently, my band was invited to play for a celebration. When the bus pulled up to the flagpole in front of my high school, I had the strangest feeling. Something was missing. I found myself nervously searching for my mom in the parking lot. I needed to tell her I didn't need a ride home; I was going out. I then realized my mother was at home and probably in bed. I never realized how much I took her for granted until she wasn't there. When I got home that night, I woke her up and told her I loved her and I missed her. I told my mom that I really appreciated all the times she had driven me back and forth. I told her I was glad she embarrassed me all those times, because I knew that it just meant she loved me, too. My mom looked back at me with tears and a big smile. The author realized his mother's love when   _  .
A. he was a child
B. he graduated from senior high school
C. he couldn't find her one day
D. his mother was sleeping
Answer: