完成下列各题 B Joseph Lemasolai wrote a book about his life. His people, the Maasai, are nomads,meaning they do not stay in one place for long. They move their villages in search of good grassand fresh water for their cattle. "The cow is the centerpiece of pretty much everything we do,"Joseph explains．“That s why we move．We could not be nomads without cattle．You can’t move for nothing--you can’t just walk around． When he was very young，Joseph spent much of his time looking after his family’s cattle，taking them to food and water and watching out for lions．He played on the grassland with his friends． when Joseph was about six years old，he left his family to attend a boarding school(寄宿学校)．There，Joseph faced difficulties much like other children do．He was laughed at because he was fat．He got into trouble daily with his teachers． But Joseph also faced difficulty most children do not．”Every time school closed for vocation，I had to find my way home，“Joseph says，”That was one of the hardest things：“The village might be 5 miles a way．or it might be 50．Sometimes I wouldn’t know exactly where my family was．I had to search for them．” Joseph later attended high school in a city．After graduation，he went to college．Finally，he became a social studies teacher，and now he is teaching seventh and eighth graders at a school． Every summer，Joseph travels back to the grassland to visit his mother，brothers，and friends．And he takes a group of students with him to see both the beauty and the difficulty of growing up in that part of the country．“I like to show them the other side of the coin．”Joseph says． The word“centerpiece’’in Paragraph l means“________”．

A. the most important part
B. the things already done
C. the reason of moving
D. the animal in the middle