Which of the following statements concerning a B+ tree of order M is TRUE?
- A. the root always has between 2 and M children
- B. not all leaves are at the same depth
- C. leaves and nonleaf nodes have some key values in common
- D. all nonleaf nodes have between ⌈M/2⌉ and M children
这道题选C,A选项没考虑只有根的情况，B很明显的错误，B+树的性质就是所有叶子节点都在同一深度，D选项错在没考虑根节点的特殊情况