People say that a mother's love knows no boundaries. This is true when it comes to my mother. She has given up many things so that my sisters and I could live a better life.  My mother comes from a large family and her parents died when she was quite young. She dropped out of school when she was fifteen because no one could afford to pay her studies. At the age of 19, she married my father and when they had my sisters and I, they moved to the United States so that we could have a better life. My parents did not know English but somehow they communicated with other people. My mother stayed at home and raised us while my father was working. There were so many dangerous incidents that happened where we lived that my mother finally decided that we all moved to Texas when I was seven.  My mother has worked so hard to give us everything. She always tells us that all she wants is for us to be happy.  As the saying goes, "You don't appreciate something until it's gone." Well, I finally had a chance to experience it. My mother went to Mexico this winter because she needed to have an operation. For the first time in my life, my mother was not there to hold and comfort me. Those two weeks when she was away made me realize how much I love her. All she has done for me is incredible. When I suffer she suffers with me. I have to show her how much I care about her. She means the world to me. The writer didn't realize that he loves his mother very much until   _  .
they moved to Texas his mother told them all she wanted was for them to be happy his mother left home for an operation his mother died
Question: People say that a mother's love knows no boundaries. This is true when it comes to my mother. She has given up many things so that my sisters and I could live a better life.  My mother comes from a large family and her parents died when she was quite young. She dropped out of school when she was fifteen because no one could afford to pay her studies. At the age of 19, she married my father and when they had my sisters and I, they moved to the United States so that we could have a better life. My parents did not know English but somehow they communicated with other people. My mother stayed at home and raised us while my father was working. There were so many dangerous incidents that happened where we lived that my mother finally decided that we all moved to Texas when I was seven.  My mother has worked so hard to give us everything. She always tells us that all she wants is for us to be happy.  As the saying goes, "You don't appreciate something until it's gone." Well, I finally had a chance to experience it. My mother went to Mexico this winter because she needed to have an operation. For the first time in my life, my mother was not there to hold and comfort me. Those two weeks when she was away made me realize how much I love her. All she has done for me is incredible. When I suffer she suffers with me. I have to show her how much I care about her. She means the world to me. The writer didn't realize that he loves his mother very much until   _  .
A. they moved to Texas
B. his mother told them all she wanted was for them to be happy
C. his mother left home for an operation
D. his mother died
Answer: