A:过点A、B作直线AB
B:以O为圆心作弧
C:在射线AM上截取AB=a
D:延长线段AB到D,使DB=AB
-- _______ the Internet ___________ in your school?
-- Yes, but the computer in our office has broken down.
下列细胞结构中属于动物和植物细胞所共有的是( )